1 \documentclass[a4paper,leqno]{strayman}
3 \let\numberwithin=\notdef
11 \renewcommand{\ge}{\geqslant}
12 \renewcommand{\le}{\leqslant}
13 \newcommand{\nge}{\ngeqslant}
14 \newcommand{\nle}{\nleqslant}
16 \newcommand{\has}{\sqsupseteq}
17 \newcommand{\isin}{\sqsubseteq}
19 \newcommand{\nothaspatch}{\mathrel{\,\not\!\not\relax\haspatch}}
20 \newcommand{\notpatchisin}{\mathrel{\,\not\!\not\relax\patchisin}}
21 \newcommand{\haspatch}{\sqSupset}
22 \newcommand{\patchisin}{\sqSubset}
24 \newif\ifhidehack\hidehackfalse
25 \DeclareRobustCommand\hidefromedef[2]{%
26 \hidehacktrue\ifhidehack#1\else#2\fi\hidehackfalse}
27 \newcommand{\pa}[1]{\hidefromedef{\varmathbb{#1}}{#1}}
29 \newcommand{\set}[1]{\mathbb{#1}}
30 \newcommand{\pay}[1]{\pa{#1}^+}
31 \newcommand{\pan}[1]{\pa{#1}^-}
33 \newcommand{\p}{\pa{P}}
34 \newcommand{\py}{\pay{P}}
35 \newcommand{\pn}{\pan{P}}
37 \newcommand{\pq}{\pa{Q}}
38 \newcommand{\pqy}{\pay{Q}}
39 \newcommand{\pqn}{\pan{Q}}
41 \newcommand{\pr}{\pa{R}}
42 \newcommand{\pry}{\pay{R}}
43 \newcommand{\prn}{\pan{R}}
45 %\newcommand{\hasparents}{\underaccent{1}{>}}
46 %\newcommand{\hasparents}{{%
47 % \declareslashed{}{_{_1}}{0}{-0.8}{>}\slashed{>}}}
48 \newcommand{\hasparents}{>_{\mkern-7.0mu _1}}
49 \newcommand{\areparents}{<_{\mkern-14.0mu _1\mkern+5.0mu}}
51 \renewcommand{\implies}{\Rightarrow}
52 \renewcommand{\equiv}{\Leftrightarrow}
53 \renewcommand{\nequiv}{\nLeftrightarrow}
54 \renewcommand{\land}{\wedge}
55 \renewcommand{\lor}{\vee}
57 \newcommand{\pancs}{{\mathcal A}}
58 \newcommand{\pends}{{\mathcal E}}
60 \newcommand{\pancsof}[2]{\pancs ( #1 , #2 ) }
61 \newcommand{\pendsof}[2]{\pends ( #1 , #2 ) }
63 \newcommand{\merge}{{\mathcal M}}
64 \newcommand{\mergeof}[4]{\merge(#1,#2,#3,#4)}
65 %\newcommand{\merge}[4]{{#2 {{\frac{ #1 }{ #3 } #4}}}}
67 \newcommand{\patch}{{\mathcal P}}
68 \newcommand{\base}{{\mathcal B}}
70 \newcommand{\patchof}[1]{\patch ( #1 ) }
71 \newcommand{\baseof}[1]{\base ( #1 ) }
73 \newcommand{\eqntag}[2]{ #2 \tag*{\mbox{#1}} }
74 \newcommand{\eqn}[2]{ #2 \tag*{\mbox{\bf #1}} }
76 %\newcommand{\bigforall}{\mathop{\hbox{\huge$\forall$}}}
77 \newcommand{\bigforall}{%
79 {\hbox{\huge$\forall$}}%
80 {\hbox{\Large$\forall$}}%
81 {\hbox{\normalsize$\forall$}}%
82 {\hbox{\scriptsize$\forall$}}}%
85 \newcommand{\Largeexists}{\mathop{\hbox{\Large$\exists$}}}
86 \newcommand{\Largenexists}{\mathop{\hbox{\Large$\nexists$}}}
88 \newcommand{\qed}{\square}
89 \newcommand{\proofstarts}{{\it Proof:}}
90 \newcommand{\proof}[1]{\proofstarts #1 $\qed$}
92 \newcommand{\gathbegin}{\begin{gather} \tag*{}}
93 \newcommand{\gathnext}{\\ \tag*{}}
96 \newcommand{\false}{f}
102 \begin{basedescript}{
104 \desclabelstyle{\nextlinelabel}
106 \item[ $ C \hasparents \set X $ ]
107 The parents of commit $C$ are exactly the set
111 $C$ is a descendant of $D$ in the git commit
112 graph. This is a partial order, namely the transitive closure of
113 $ D \in \set X $ where $ C \hasparents \set X $.
115 \item[ $ C \has D $ ]
116 Informally, the tree at commit $C$ contains the change
117 made in commit $D$. Does not take account of deliberate reversions by
118 the user or reversion, rebasing or rewinding in
119 non-Topbloke-controlled branches. For merges and Topbloke-generated
120 anticommits or re-commits, the ``change made'' is only to be thought
121 of as any conflict resolution. This is not a partial order because it
124 \item[ $ \p, \py, \pn $ ]
125 A patch $\p$ consists of two sets of commits $\pn$ and $\py$, which
126 are respectively the base and tip git branches. $\p$ may be used
127 where the context requires a set, in which case the statement
128 is to be taken as applying to both $\py$ and $\pn$.
129 None of these sets overlap. Hence:
131 \item[ $ \patchof{ C } $ ]
132 Either $\p$ s.t. $ C \in \p $, or $\bot$.
133 A function from commits to patches' sets $\p$.
135 \item[ $ \pancsof{C}{\set P} $ ]
136 $ \{ A \; | \; A \le C \land A \in \set P \} $
137 i.e. all the ancestors of $C$
138 which are in $\set P$.
140 \item[ $ \pendsof{C}{\set P} $ ]
141 $ \{ E \; | \; E \in \pancsof{C}{\set P}
142 \land \mathop{\not\exists}_{A \in \pancsof{C}{\set P}}
143 E \neq A \land E \le A \} $
144 i.e. all $\le$-maximal commits in $\pancsof{C}{\set P}$.
146 \item[ $ \baseof{C} $ ]
147 $ \pendsof{C}{\pn} = \{ \baseof{C} \} $ where $ C \in \py $.
148 A partial function from commits to commits.
149 See Unique Base, below.
151 \item[ $ C \haspatch \p $ ]
152 $\displaystyle \bigforall_{D \in \py} D \isin C \equiv D \le C $.
153 ~ Informally, $C$ has the contents of $\p$.
155 \item[ $ C \nothaspatch \p $ ]
156 $\displaystyle \bigforall_{D \in \py} D \not\isin C $.
157 ~ Informally, $C$ has none of the contents of $\p$.
159 Non-Topbloke commits are $\nothaspatch \p$ for all $\p$. This
160 includes commits on plain git branches made by applying a Topbloke
162 patch is applied to a non-Topbloke branch and then bubbles back to
163 the relevant Topbloke branches, we hope that
164 if the user still cares about the Topbloke patch,
165 git's merge algorithm will DTRT when trying to re-apply the changes.
167 \item[ $\displaystyle \mergeof{C}{L}{M}{R} $ ]
168 The contents of a git merge result:
170 $\displaystyle D \isin C \equiv
172 (D \isin L \land D \isin R) \lor D = C : & \true \\
173 (D \not\isin L \land D \not\isin R) \land D \neq C : & \false \\
174 \text{otherwise} : & D \not\isin M
182 We maintain these each time we construct a new commit. \\
184 C \has D \implies C \ge D
186 \[\eqn{Unique Base:}{
187 \bigforall_{C \in \py} \pendsof{C}{\pn} = \{ B \}
189 \[\eqn{Tip Contents:}{
190 \bigforall_{C \in \py} D \isin C \equiv
191 { D \isin \baseof{C} \lor \atop
192 (D \in \py \land D \le C) }
194 \[\eqn{Base Acyclic:}{
195 \bigforall_{B \in \pn} D \isin B \implies D \notin \py
198 \bigforall_{C,\p} C \haspatch \p \lor C \nothaspatch \p
200 \[\eqn{Foreign Inclusion:}{
201 \bigforall_{D \text{ s.t. } \patchof{D} = \bot} D \isin C \equiv D \leq C
203 \[\eqn{Foreign Contents:}{
204 \bigforall_{C \text{ s.t. } \patchof{C} = \bot}
205 D \le C \implies \patchof{D} = \bot
208 \section{Some lemmas}
210 \[ \eqn{Alternative (overlapping) formulations defining
211 $\mergeof{C}{L}{M}{R}$:}{
214 D \isin L \equiv D \isin R : & D = C \lor D \isin L \\
215 D \isin L \nequiv D \isin R : & D = C \lor D \not\isin M \\
216 D \isin L \equiv D \isin M : & D = C \lor D \isin R \\
217 D \isin L \nequiv D \isin M : & D = C \lor D \isin L \\
218 \text{as above with L and R exchanged}
224 Original definition is symmetrical in $L$ and $R$.
227 \[ \eqn{Exclusive Tip Contents:}{
228 \bigforall_{C \in \py}
229 \neg \Bigl[ D \isin \baseof{C} \land ( D \in \py \land D \le C )
232 Ie, the two limbs of the RHS of Tip Contents are mutually exclusive.
235 Let $B = \baseof{C}$ in $D \isin \baseof{C}$. Now $B \in \pn$.
236 So by Base Acyclic $D \isin B \implies D \notin \py$.
238 \[ \eqntag{{\it Corollary - equivalent to Tip Contents}}{
239 \bigforall_{C \in \py} D \isin C \equiv
241 D \in \py : & D \le C \\
242 D \not\in \py : & D \isin \baseof{C}
246 \[ \eqn{Tip Self Inpatch:}{
247 \bigforall_{C \in \py} C \haspatch \p
249 Ie, tip commits contain their own patch.
252 Apply Exclusive Tip Contents to some $D \in \py$:
253 $ \bigforall_{C \in \py}\bigforall_{D \in \py}
254 D \isin C \equiv D \le C $
257 \[ \eqn{Exact Ancestors:}{
258 \bigforall_{ C \hasparents \set{R} }
260 ( \mathop{\hbox{\huge{$\vee$}}}_{R \in \set R} D \le R )
265 \[ \eqn{Transitive Ancestors:}{
266 \left[ \bigforall_{ E \in \pendsof{C}{\set P} } E \le M \right] \equiv
267 \left[ \bigforall_{ A \in \pancsof{C}{\set P} } A \le M \right]
271 The implication from right to left is trivial because
272 $ \pends() \subset \pancs() $.
273 For the implication from left to right:
274 by the definition of $\mathcal E$,
275 for every such $A$, either $A \in \pends()$ which implies
276 $A \le M$ by the LHS directly,
277 or $\exists_{A' \in \pancs()} \; A' \neq A \land A \le A' $
278 in which case we repeat for $A'$. Since there are finitely many
279 commits, this terminates with $A'' \in \pends()$, ie $A'' \le M$
280 by the LHS. And $A \le A''$.
283 \[ \eqn{Calculation Of Ends:}{
284 \bigforall_{C \hasparents \set A}
285 \pendsof{C}{\set P} =
289 C \not\in \p : & \displaystyle
291 \Bigl[ \Largeexists_{A \in \set A}
292 E \in \pendsof{A}{\set P} \Bigr] \land
293 \Bigl[ \Largenexists_{B \in \set A}
294 E \neq B \land E \le B \Bigr]
300 \[ \eqn{Ingredients Prevent Replay:}{
302 {C \hasparents \set A} \land
307 \Largeexists_{A \in \set A} D \isin A
309 \right] \implies \left[
310 D \isin C \implies D \le C
314 Trivial for $D = C$. Consider some $D \neq C$, $D \isin C$.
315 By the preconditions, there is some $A$ s.t. $D \in \set A$
316 and $D \isin A$. By No Replay for $A$, $D \le A$. And
317 $A \le C$ so $D \le C$.
320 \[ \eqn{Totally Foreign Contents:}{
321 \bigforall_{C \hasparents \set A}
323 \patchof{C} = \bot \land
324 \bigforall_{A \in \set A} \patchof{A} = \bot
334 Consider some $D \le C$. If $D = C$, $\patchof{D} = \bot$ trivially.
335 If $D \neq C$ then $D \le A$ where $A \in \set A$. By Foreign
336 Contents of $A$, $\patchof{D} = \bot$.
339 \section{Commit annotation}
341 We annotate each Topbloke commit $C$ with:
345 \baseof{C}, \text{ if } C \in \py
348 \text{ either } C \haspatch \pq \text{ or } C \nothaspatch \pq
350 \bigforall_{\pqy \not\ni C} \pendsof{C}{\pqy}
353 $\patchof{C}$, for each kind of Topbloke-generated commit, is stated
354 in the summary in the section for that kind of commit.
356 Whether $\baseof{C}$ is required, and if so what the value is, is
357 stated in the proof of Unique Base for each kind of commit.
359 $C \haspatch \pq$ or $\nothaspatch \pq$ is represented as the
360 set $\{ \pq | C \haspatch \pq \}$. Whether $C \haspatch \pq$
362 (in terms of $I \haspatch \pq$ or $I \nothaspatch \pq$
363 for the ingredients $I$),
364 in the proof of Coherence for each kind of commit.
366 $\pendsof{C}{\pq^+}$ is computed, for all Topbloke-generated commits,
367 using the lemma Calculation of Ends, above.
368 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
369 make it wrong to make plain commits with git because the recorded $\pends$
370 would have to be updated. The annotation is not needed in that case
371 because $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
373 \section{Simple commit}
375 A simple single-parent forward commit $C$ as made by git-commit.
377 \tag*{} C \hasparents \{ A \} \\
378 \tag*{} \patchof{C} = \patchof{A} \\
379 \tag*{} D \isin C \equiv D \isin A \lor D = C
381 This also covers Topbloke-generated commits on plain git branches:
382 Topbloke strips the metadata when exporting.
384 \subsection{No Replay}
386 Ingredients Prevent Replay applies. $\qed$
388 \subsection{Unique Base}
389 If $A, C \in \py$ then by Calculation of Ends for
390 $C, \py, C \not\in \py$:
391 $\pendsof{C}{\pn} = \pendsof{A}{\pn}$ so
392 $\baseof{C} = \baseof{A}$. $\qed$
394 \subsection{Tip Contents}
395 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
396 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
397 Substitute into the contents of $C$:
398 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
400 Since $D = C \implies D \in \py$,
401 and substituting in $\baseof{C}$, this gives:
402 \[ D \isin C \equiv D \isin \baseof{C} \lor
403 (D \in \py \land D \le A) \lor
404 (D = C \land D \in \py) \]
405 \[ \equiv D \isin \baseof{C} \lor
406 [ D \in \py \land ( D \le A \lor D = C ) ] \]
407 So by Exact Ancestors:
408 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
412 \subsection{Base Acyclic}
414 Need to consider only $A, C \in \pn$.
416 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
418 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
419 $A$, $D \isin C \implies D \not\in \py$.
423 \subsection{Coherence and patch inclusion}
425 Need to consider $D \in \py$
427 \subsubsection{For $A \haspatch P, D = C$:}
433 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
435 \subsubsection{For $A \haspatch P, D \neq C$:}
436 Ancestors: $ D \le C \equiv D \le A $.
438 Contents: $ D \isin C \equiv D \isin A \lor f $
439 so $ D \isin C \equiv D \isin A $.
442 \[ A \haspatch P \implies C \haspatch P \]
444 \subsubsection{For $A \nothaspatch P$:}
446 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
449 Now by contents of $A$, $D \notin A$, so $D \notin C$.
452 \[ A \nothaspatch P \implies C \nothaspatch P \]
455 \subsection{Foreign inclusion:}
457 If $D = C$, trivial. For $D \neq C$:
458 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
460 \subsection{Foreign Contents:}
462 Only relevant if $\patchof{C} = \bot$, and in that case Totally
463 Foreign Contents applies. $\qed$
465 \section{Create Base}
467 Given $L$, create a Topbloke base branch initial commit $B$.
469 B \hasparents \{ L \}
473 D \isin B \equiv D \isin L \lor D = B
476 \subsection{Conditions}
478 \[ \eqn{ Ingredients }{
479 \patchof{L} = \pa{L} \lor \patchof{L} = \bot
481 \[ \eqn{ Create Acyclic }{
485 \subsection{No Replay}
487 Ingredients Prevent Replay applies. $\qed$
489 \subsection{Unique Base}
493 \subsection{Tip Contents}
497 \subsection{Base Acyclic}
499 Consider some $D \isin B$. If $D = B$, $D \in \pqn$.
500 If $D \neq B$, $D \isin L$, and by Create Acyclic
501 $D \not\in \pqy$. $\qed$
503 \subsection{Coherence and Patch Inclusion}
505 Consider some $D \in \p$.
506 $B \not\in \py$ so $D \neq B$. So $D \isin B \equiv D \isin L$.
508 Thus $L \haspatch \p \implies B \haspatch P$
509 and $L \nothaspatch \p \implies B \nothaspatch P$.
513 \subsection{Foreign Inclusion}
515 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq B$
516 so $D \isin B \equiv D \isin L$.
517 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
518 And by Exact Ancestors $D \le L \equiv D \le B$.
519 So $D \isin B \equiv D \le B$. $\qed$
521 \subsection{Foreign Contents}
527 Given a Topbloke base $B$, create a tip branch initial commit B.
529 C \hasparents \{ B \}
533 D \isin C \equiv D \isin B \lor D = C
536 \subsection{Conditions}
538 \[ \eqn{ Ingredients }{
542 \pendsof{B}{\pqy} = \{ \}
545 \subsection{No Replay}
547 Ingredients Prevent Replay applies. $\qed$
549 \subsection{Unique Base}
551 Trivially, $\pendsof{C}{\pqn} = \{B\}$ so $\baseof{C} = B$.
553 \subsection{Tip Contents}
555 Consider some arbitrary commit $D$. If $D = C$, trivially satisfied.
557 If $D \neq C$, $D \isin C \equiv D \isin B$.
558 By Base Acyclic of $B$, $D \isin B \implies D \not\in \pqy$.
559 So $D \isin C \equiv D \isin \baseof{B}$.
563 \subsection{Base Acyclic}
567 \subsection{Coherence and Patch Inclusion}
569 Consider some $D \in \py$.
571 \subsubsection{For $\p = \pq$:}
573 By Base Acyclic, $D \not\isin B$. So $D \isin C \equiv D = C$.
574 By No Sneak, $D \le B \equiv D = C$. Thus $C \haspatch \pq$.
580 Given $L$ and $\pr$ as represented by $R^+, R^-$.
581 Construct $C$ which has $\pr$ removed.
582 Used for removing a branch dependency.
584 C \hasparents \{ L \}
586 \patchof{C} = \patchof{L}
588 \mergeof{C}{L}{R^+}{R^-}
591 \subsection{Conditions}
593 \[ \eqn{ Ingredients }{
594 R^+ \in \pry \land R^- = \baseof{R^+}
596 \[ \eqn{ Into Base }{
599 \[ \eqn{ Unique Tip }{
600 \pendsof{L}{\pry} = \{ R^+ \}
602 \[ \eqn{ Currently Included }{
606 \subsection{Ordering of Ingredients:}
608 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
609 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
612 (Note that $R^+ \not\le R^-$, i.e. the merge base
613 is a descendant, not an ancestor, of the 2nd parent.)
615 \subsection{No Replay}
617 By definition of $\merge$,
618 $D \isin C \implies D \isin L \lor D \isin R^- \lor D = C$.
619 So, by Ordering of Ingredients,
620 Ingredients Prevent Replay applies. $\qed$
622 \subsection{Desired Contents}
624 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
627 \subsubsection{For $D = C$:}
629 Trivially $D \isin C$. OK.
631 \subsubsection{For $D \neq C, D \not\le L$:}
633 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
634 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
636 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
638 By Currently Included, $D \isin L$.
640 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
641 by Unique Tip, $D \le R^+ \equiv D \le L$.
644 By Base Acyclic, $D \not\isin R^-$.
646 Apply $\merge$: $D \not\isin C$. OK.
648 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
650 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
652 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
656 \subsection{Unique Base}
658 Into Base means that $C \in \pn$, so Unique Base is not
661 \subsection{Tip Contents}
663 Again, not applicable. $\qed$
665 \subsection{Base Acyclic}
667 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
668 And by Into Base $C \not\in \py$.
669 Now from Desired Contents, above, $D \isin C
670 \implies D \isin L \lor D = C$, which thus
671 $\implies D \not\in \py$. $\qed$.
673 \subsection{Coherence and Patch Inclusion}
675 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
677 \subsubsection{For $\p = \pr$:}
678 By Desired Contents, above, $D \not\isin C$.
679 So $C \nothaspatch \pr$.
681 \subsubsection{For $\p \neq \pr$:}
682 By Desired Contents, $D \isin C \equiv D \isin L$
683 (since $D \in \py$ so $D \not\in \pry$).
685 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
686 So $L \nothaspatch \p \implies C \nothaspatch \p$.
688 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
689 so $L \haspatch \p \implies C \haspatch \p$.
693 \subsection{Foreign Inclusion}
695 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
696 So by Desired Contents $D \isin C \equiv D \isin L$.
697 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
699 And $D \le C \equiv D \le L$.
700 Thus $D \isin C \equiv D \le C$.
704 \subsection{Foreign Contents}
710 Merge commits $L$ and $R$ using merge base $M$:
712 C \hasparents \{ L, R \}
714 \patchof{C} = \patchof{L}
718 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
720 \subsection{Conditions}
721 \[ \eqn{ Ingredients }{
724 \[ \eqn{ Tip Merge }{
727 R \in \py : & \baseof{R} \ge \baseof{L}
728 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
729 R \in \pn : & M = \baseof{L} \\
730 \text{otherwise} : & \false
733 \[ \eqn{ Merge Acyclic }{
738 \[ \eqn{ Removal Merge Ends }{
739 X \not\haspatch \p \land
743 \pendsof{Y}{\py} = \pendsof{M}{\py}
745 \[ \eqn{ Addition Merge Ends }{
746 X \not\haspatch \p \land
750 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
753 \[ \eqn{ Foreign Merges }{
754 \patchof{L} = \bot \equiv \patchof{R} = \bot
757 \subsection{Non-Topbloke merges}
759 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$
760 (Foreign Merges, above).
761 I.e. not only is it forbidden to merge into a Topbloke-controlled
762 branch without Topbloke's assistance, it is also forbidden to
763 merge any Topbloke-controlled branch into any plain git branch.
765 Given those conditions, Tip Merge and Merge Acyclic do not apply.
766 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
767 Merge Ends condition applies.
769 So a plain git merge of non-Topbloke branches meets the conditions and
770 is therefore consistent with our scheme.
772 \subsection{No Replay}
774 By definition of $\merge$,
775 $D \isin C \implies D \isin L \lor D \isin R \lor D = C$.
777 Ingredients Prevent Replay applies. $\qed$
779 \subsection{Unique Base}
781 Need to consider only $C \in \py$, ie $L \in \py$,
782 and calculate $\pendsof{C}{\pn}$. So we will consider some
783 putative ancestor $A \in \pn$ and see whether $A \le C$.
785 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
786 But $C \in py$ and $A \in \pn$ so $A \neq C$.
787 Thus $A \le C \equiv A \le L \lor A \le R$.
789 By Unique Base of L and Transitive Ancestors,
790 $A \le L \equiv A \le \baseof{L}$.
792 \subsubsection{For $R \in \py$:}
794 By Unique Base of $R$ and Transitive Ancestors,
795 $A \le R \equiv A \le \baseof{R}$.
797 But by Tip Merge condition on $\baseof{R}$,
798 $A \le \baseof{L} \implies A \le \baseof{R}$, so
799 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
800 Thus $A \le C \equiv A \le \baseof{R}$.
801 That is, $\baseof{C} = \baseof{R}$.
803 \subsubsection{For $R \in \pn$:}
805 By Tip Merge condition on $R$ and since $M \le R$,
806 $A \le \baseof{L} \implies A \le R$, so
807 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
808 Thus $A \le C \equiv A \le R$.
809 That is, $\baseof{C} = R$.
813 \subsection{Coherence and Patch Inclusion}
815 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
816 This involves considering $D \in \py$.
818 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
819 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
820 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
821 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
823 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
824 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
825 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
827 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
829 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
830 \equiv D \isin L \lor D \isin R$.
831 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
833 Consider $D \neq C, D \isin X \land D \isin Y$:
834 By $\merge$, $D \isin C$. Also $D \le X$
835 so $D \le C$. OK for $C \haspatch \p$.
837 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
838 By $\merge$, $D \not\isin C$.
839 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
840 OK for $C \haspatch \p$.
842 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
843 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
844 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
845 OK for $C \haspatch \p$.
847 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
849 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
851 $M \haspatch \p \implies C \nothaspatch \p$.
852 $M \nothaspatch \p \implies C \haspatch \p$.
856 One of the Merge Ends conditions applies.
857 Recall that we are considering $D \in \py$.
858 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
859 We will show for each of
860 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
861 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
863 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
864 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
865 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
866 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
868 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
869 $D \le Y$ so $D \le C$.
870 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
872 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
873 $D \not\le Y$. If $D \le X$ then
874 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
875 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
876 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
878 Consider $D \neq C, M \haspatch P, D \isin Y$:
879 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
880 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
881 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
883 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
884 By $\merge$, $D \not\isin C$. OK.
888 \subsection{Base Acyclic}
890 This applies when $C \in \pn$.
891 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
893 Consider some $D \in \py$.
895 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
896 R$. And $D \neq C$. So $D \not\isin C$.
900 \subsection{Tip Contents}
902 We need worry only about $C \in \py$.
903 And $\patchof{C} = \patchof{L}$
904 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
905 of $C$, and its Coherence and Patch Inclusion, as just proved.
907 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
908 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
909 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
910 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
911 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
913 We will consider an arbitrary commit $D$
914 and prove the Exclusive Tip Contents form.
916 \subsubsection{For $D \in \py$:}
917 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
920 \subsubsection{For $D \not\in \py, R \not\in \py$:}
922 $D \neq C$. By Tip Contents of $L$,
923 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
924 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
925 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
926 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
928 \subsubsection{For $D \not\in \py, R \in \py$:}
933 $D \isin L \equiv D \isin \baseof{L}$ and
934 $D \isin R \equiv D \isin \baseof{R}$.
936 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
937 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
938 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
939 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
941 So $D \isin M \equiv D \isin L$ and by $\merge$,
942 $D \isin C \equiv D \isin R$. But from Unique Base,
943 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
947 \subsection{Foreign Inclusion}
949 Consider some $D$ s.t. $\patchof{D} = \bot$.
950 By Foreign Inclusion of $L, M, R$:
951 $D \isin L \equiv D \le L$;
952 $D \isin M \equiv D \le M$;
953 $D \isin R \equiv D \le R$.
955 \subsubsection{For $D = C$:}
957 $D \isin C$ and $D \le C$. OK.
959 \subsubsection{For $D \neq C, D \isin M$:}
961 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
962 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
964 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
966 By $\merge$, $D \isin C$.
967 And $D \isin X$ means $D \le X$ so $D \le C$.
970 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
972 By $\merge$, $D \not\isin C$.
973 And $D \not\le L, D \not\le R$ so $D \not\le C$.
978 \subsection{Foreign Contents}
980 Only relevant if $\patchof{L} = \bot$, in which case
981 $\patchof{C} = \bot$ and by Foreign Merges $\patchof{R} = \bot$,
982 so Totally Foreign Contents applies. $\qed$