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 \subsection{No Replay}
544 Ingredients Prevent Replay applies. $\qed$
546 \subsection{Unique Base}
548 Trivially, $\pendsof{C}{\pqn} = \{B\}$ so $\baseof{C} = B$.
550 \subsection{Tip Contents}
552 Consider some arbitrary commit $D$. If $D = C$, trivially satisfied.
554 If $D \neq C$, $D \isin C \equiv D \isin B$.
555 By Base Acyclic of $B$, $D \isin B \implies D \not\in \pqy$.
556 So $D \isin C \equiv D \isin \baseof{B}$.
564 Given $L$ and $\pr$ as represented by $R^+, R^-$.
565 Construct $C$ which has $\pr$ removed.
566 Used for removing a branch dependency.
568 C \hasparents \{ L \}
570 \patchof{C} = \patchof{L}
572 \mergeof{C}{L}{R^+}{R^-}
575 \subsection{Conditions}
577 \[ \eqn{ Ingredients }{
578 R^+ \in \pry \land R^- = \baseof{R^+}
580 \[ \eqn{ Into Base }{
583 \[ \eqn{ Unique Tip }{
584 \pendsof{L}{\pry} = \{ R^+ \}
586 \[ \eqn{ Currently Included }{
590 \subsection{Ordering of Ingredients:}
592 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
593 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
596 (Note that $R^+ \not\le R^-$, i.e. the merge base
597 is a descendant, not an ancestor, of the 2nd parent.)
599 \subsection{No Replay}
601 By definition of $\merge$,
602 $D \isin C \implies D \isin L \lor D \isin R^- \lor D = C$.
603 So, by Ordering of Ingredients,
604 Ingredients Prevent Replay applies. $\qed$
606 \subsection{Desired Contents}
608 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
611 \subsubsection{For $D = C$:}
613 Trivially $D \isin C$. OK.
615 \subsubsection{For $D \neq C, D \not\le L$:}
617 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
618 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
620 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
622 By Currently Included, $D \isin L$.
624 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
625 by Unique Tip, $D \le R^+ \equiv D \le L$.
628 By Base Acyclic, $D \not\isin R^-$.
630 Apply $\merge$: $D \not\isin C$. OK.
632 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
634 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
636 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
640 \subsection{Unique Base}
642 Into Base means that $C \in \pn$, so Unique Base is not
645 \subsection{Tip Contents}
647 Again, not applicable. $\qed$
649 \subsection{Base Acyclic}
651 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
652 And by Into Base $C \not\in \py$.
653 Now from Desired Contents, above, $D \isin C
654 \implies D \isin L \lor D = C$, which thus
655 $\implies D \not\in \py$. $\qed$.
657 \subsection{Coherence and Patch Inclusion}
659 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
661 \subsubsection{For $\p = \pr$:}
662 By Desired Contents, above, $D \not\isin C$.
663 So $C \nothaspatch \pr$.
665 \subsubsection{For $\p \neq \pr$:}
666 By Desired Contents, $D \isin C \equiv D \isin L$
667 (since $D \in \py$ so $D \not\in \pry$).
669 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
670 So $L \nothaspatch \p \implies C \nothaspatch \p$.
672 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
673 so $L \haspatch \p \implies C \haspatch \p$.
677 \subsection{Foreign Inclusion}
679 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
680 So by Desired Contents $D \isin C \equiv D \isin L$.
681 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
683 And $D \le C \equiv D \le L$.
684 Thus $D \isin C \equiv D \le C$.
688 \subsection{Foreign Contents}
694 Merge commits $L$ and $R$ using merge base $M$:
696 C \hasparents \{ L, R \}
698 \patchof{C} = \patchof{L}
702 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
704 \subsection{Conditions}
705 \[ \eqn{ Ingredients }{
708 \[ \eqn{ Tip Merge }{
711 R \in \py : & \baseof{R} \ge \baseof{L}
712 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
713 R \in \pn : & M = \baseof{L} \\
714 \text{otherwise} : & \false
717 \[ \eqn{ Merge Acyclic }{
722 \[ \eqn{ Removal Merge Ends }{
723 X \not\haspatch \p \land
727 \pendsof{Y}{\py} = \pendsof{M}{\py}
729 \[ \eqn{ Addition Merge Ends }{
730 X \not\haspatch \p \land
734 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
737 \[ \eqn{ Foreign Merges }{
738 \patchof{L} = \bot \equiv \patchof{R} = \bot
741 \subsection{Non-Topbloke merges}
743 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$
744 (Foreign Merges, above).
745 I.e. not only is it forbidden to merge into a Topbloke-controlled
746 branch without Topbloke's assistance, it is also forbidden to
747 merge any Topbloke-controlled branch into any plain git branch.
749 Given those conditions, Tip Merge and Merge Acyclic do not apply.
750 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
751 Merge Ends condition applies.
753 So a plain git merge of non-Topbloke branches meets the conditions and
754 is therefore consistent with our scheme.
756 \subsection{No Replay}
758 By definition of $\merge$,
759 $D \isin C \implies D \isin L \lor D \isin R \lor D = C$.
761 Ingredients Prevent Replay applies. $\qed$
763 \subsection{Unique Base}
765 Need to consider only $C \in \py$, ie $L \in \py$,
766 and calculate $\pendsof{C}{\pn}$. So we will consider some
767 putative ancestor $A \in \pn$ and see whether $A \le C$.
769 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
770 But $C \in py$ and $A \in \pn$ so $A \neq C$.
771 Thus $A \le C \equiv A \le L \lor A \le R$.
773 By Unique Base of L and Transitive Ancestors,
774 $A \le L \equiv A \le \baseof{L}$.
776 \subsubsection{For $R \in \py$:}
778 By Unique Base of $R$ and Transitive Ancestors,
779 $A \le R \equiv A \le \baseof{R}$.
781 But by Tip Merge condition on $\baseof{R}$,
782 $A \le \baseof{L} \implies A \le \baseof{R}$, so
783 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
784 Thus $A \le C \equiv A \le \baseof{R}$.
785 That is, $\baseof{C} = \baseof{R}$.
787 \subsubsection{For $R \in \pn$:}
789 By Tip Merge condition on $R$ and since $M \le R$,
790 $A \le \baseof{L} \implies A \le R$, so
791 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
792 Thus $A \le C \equiv A \le R$.
793 That is, $\baseof{C} = R$.
797 \subsection{Coherence and Patch Inclusion}
799 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
800 This involves considering $D \in \py$.
802 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
803 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
804 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
805 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
807 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
808 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
809 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
811 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
813 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
814 \equiv D \isin L \lor D \isin R$.
815 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
817 Consider $D \neq C, D \isin X \land D \isin Y$:
818 By $\merge$, $D \isin C$. Also $D \le X$
819 so $D \le C$. OK for $C \haspatch \p$.
821 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
822 By $\merge$, $D \not\isin C$.
823 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
824 OK for $C \haspatch \p$.
826 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
827 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
828 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
829 OK for $C \haspatch \p$.
831 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
833 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
835 $M \haspatch \p \implies C \nothaspatch \p$.
836 $M \nothaspatch \p \implies C \haspatch \p$.
840 One of the Merge Ends conditions applies.
841 Recall that we are considering $D \in \py$.
842 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
843 We will show for each of
844 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
845 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
847 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
848 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
849 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
850 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
852 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
853 $D \le Y$ so $D \le C$.
854 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
856 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
857 $D \not\le Y$. If $D \le X$ then
858 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
859 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
860 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
862 Consider $D \neq C, M \haspatch P, D \isin Y$:
863 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
864 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
865 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
867 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
868 By $\merge$, $D \not\isin C$. OK.
872 \subsection{Base Acyclic}
874 This applies when $C \in \pn$.
875 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
877 Consider some $D \in \py$.
879 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
880 R$. And $D \neq C$. So $D \not\isin C$.
884 \subsection{Tip Contents}
886 We need worry only about $C \in \py$.
887 And $\patchof{C} = \patchof{L}$
888 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
889 of $C$, and its Coherence and Patch Inclusion, as just proved.
891 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
892 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
893 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
894 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
895 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
897 We will consider an arbitrary commit $D$
898 and prove the Exclusive Tip Contents form.
900 \subsubsection{For $D \in \py$:}
901 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
904 \subsubsection{For $D \not\in \py, R \not\in \py$:}
906 $D \neq C$. By Tip Contents of $L$,
907 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
908 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
909 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
910 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
912 \subsubsection{For $D \not\in \py, R \in \py$:}
917 $D \isin L \equiv D \isin \baseof{L}$ and
918 $D \isin R \equiv D \isin \baseof{R}$.
920 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
921 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
922 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
923 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
925 So $D \isin M \equiv D \isin L$ and by $\merge$,
926 $D \isin C \equiv D \isin R$. But from Unique Base,
927 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
931 \subsection{Foreign Inclusion}
933 Consider some $D$ s.t. $\patchof{D} = \bot$.
934 By Foreign Inclusion of $L, M, R$:
935 $D \isin L \equiv D \le L$;
936 $D \isin M \equiv D \le M$;
937 $D \isin R \equiv D \le R$.
939 \subsubsection{For $D = C$:}
941 $D \isin C$ and $D \le C$. OK.
943 \subsubsection{For $D \neq C, D \isin M$:}
945 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
946 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
948 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
950 By $\merge$, $D \isin C$.
951 And $D \isin X$ means $D \le X$ so $D \le C$.
954 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
956 By $\merge$, $D \not\isin C$.
957 And $D \not\le L, D \not\le R$ so $D \not\le C$.
962 \subsection{Foreign Contents}
964 Only relevant if $\patchof{L} = \bot$, in which case
965 $\patchof{C} = \bot$ and by Foreign Merges $\patchof{R} = \bot$,
966 so Totally Foreign Contents applies. $\qed$