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{\pr}{\pa{R}}
38 \newcommand{\pry}{\pay{R}}
39 \newcommand{\prn}{\pan{R}}
41 %\newcommand{\hasparents}{\underaccent{1}{>}}
42 %\newcommand{\hasparents}{{%
43 % \declareslashed{}{_{_1}}{0}{-0.8}{>}\slashed{>}}}
44 \newcommand{\hasparents}{>_{\mkern-7.0mu _1}}
45 \newcommand{\areparents}{<_{\mkern-14.0mu _1\mkern+5.0mu}}
47 \renewcommand{\implies}{\Rightarrow}
48 \renewcommand{\equiv}{\Leftrightarrow}
49 \renewcommand{\nequiv}{\nLeftrightarrow}
50 \renewcommand{\land}{\wedge}
51 \renewcommand{\lor}{\vee}
53 \newcommand{\pancs}{{\mathcal A}}
54 \newcommand{\pends}{{\mathcal E}}
56 \newcommand{\pancsof}[2]{\pancs ( #1 , #2 ) }
57 \newcommand{\pendsof}[2]{\pends ( #1 , #2 ) }
59 \newcommand{\merge}{{\mathcal M}}
60 \newcommand{\mergeof}[4]{\merge(#1,#2,#3,#4)}
61 %\newcommand{\merge}[4]{{#2 {{\frac{ #1 }{ #3 } #4}}}}
63 \newcommand{\patch}{{\mathcal P}}
64 \newcommand{\base}{{\mathcal B}}
66 \newcommand{\patchof}[1]{\patch ( #1 ) }
67 \newcommand{\baseof}[1]{\base ( #1 ) }
69 \newcommand{\eqntag}[2]{ #2 \tag*{\mbox{#1}} }
70 \newcommand{\eqn}[2]{ #2 \tag*{\mbox{\bf #1}} }
72 %\newcommand{\bigforall}{\mathop{\hbox{\huge$\forall$}}}
73 \newcommand{\bigforall}{%
75 {\hbox{\huge$\forall$}}%
76 {\hbox{\Large$\forall$}}%
77 {\hbox{\normalsize$\forall$}}%
78 {\hbox{\scriptsize$\forall$}}}%
81 \newcommand{\Largeexists}{\mathop{\hbox{\Large$\exists$}}}
82 \newcommand{\Largenexists}{\mathop{\hbox{\Large$\nexists$}}}
84 \newcommand{\qed}{\square}
85 \newcommand{\proofstarts}{{\it Proof:}}
86 \newcommand{\proof}[1]{\proofstarts #1 $\qed$}
88 \newcommand{\gathbegin}{\begin{gather} \tag*{}}
89 \newcommand{\gathnext}{\\ \tag*{}}
92 \newcommand{\false}{f}
100 \desclabelstyle{\nextlinelabel}
102 \item[ $ C \hasparents \set X $ ]
103 The parents of commit $C$ are exactly the set
107 $C$ is a descendant of $D$ in the git commit
108 graph. This is a partial order, namely the transitive closure of
109 $ D \in \set X $ where $ C \hasparents \set X $.
111 \item[ $ C \has D $ ]
112 Informally, the tree at commit $C$ contains the change
113 made in commit $D$. Does not take account of deliberate reversions by
114 the user or reversion, rebasing or rewinding in
115 non-Topbloke-controlled branches. For merges and Topbloke-generated
116 anticommits or re-commits, the ``change made'' is only to be thought
117 of as any conflict resolution. This is not a partial order because it
120 \item[ $ \p, \py, \pn $ ]
121 A patch $\p$ consists of two sets of commits $\pn$ and $\py$, which
122 are respectively the base and tip git branches. $\p$ may be used
123 where the context requires a set, in which case the statement
124 is to be taken as applying to both $\py$ and $\pn$.
125 None of these sets overlap. Hence:
127 \item[ $ \patchof{ C } $ ]
128 Either $\p$ s.t. $ C \in \p $, or $\bot$.
129 A function from commits to patches' sets $\p$.
131 \item[ $ \pancsof{C}{\set P} $ ]
132 $ \{ A \; | \; A \le C \land A \in \set P \} $
133 i.e. all the ancestors of $C$
134 which are in $\set P$.
136 \item[ $ \pendsof{C}{\set P} $ ]
137 $ \{ E \; | \; E \in \pancsof{C}{\set P}
138 \land \mathop{\not\exists}_{A \in \pancsof{C}{\set P}}
139 E \neq A \land E \le A \} $
140 i.e. all $\le$-maximal commits in $\pancsof{C}{\set P}$.
142 \item[ $ \baseof{C} $ ]
143 $ \pendsof{C}{\pn} = \{ \baseof{C} \} $ where $ C \in \py $.
144 A partial function from commits to commits.
145 See Unique Base, below.
147 \item[ $ C \haspatch \p $ ]
148 $\displaystyle \bigforall_{D \in \py} D \isin C \equiv D \le C $.
149 ~ Informally, $C$ has the contents of $\p$.
151 \item[ $ C \nothaspatch \p $ ]
152 $\displaystyle \bigforall_{D \in \py} D \not\isin C $.
153 ~ Informally, $C$ has none of the contents of $\p$.
155 Non-Topbloke commits are $\nothaspatch \p$ for all $\p$. This
156 includes commits on plain git branches made by applying a Topbloke
158 patch is applied to a non-Topbloke branch and then bubbles back to
159 the relevant Topbloke branches, we hope that
160 if the user still cares about the Topbloke patch,
161 git's merge algorithm will DTRT when trying to re-apply the changes.
163 \item[ $\displaystyle \mergeof{C}{L}{M}{R} $ ]
164 The contents of a git merge result:
166 $\displaystyle D \isin C \equiv
168 (D \isin L \land D \isin R) \lor D = C : & \true \\
169 (D \not\isin L \land D \not\isin R) \land D \neq C : & \false \\
170 \text{otherwise} : & D \not\isin M
178 We maintain these each time we construct a new commit. \\
180 C \has D \implies C \ge D
182 \[\eqn{Unique Base:}{
183 \bigforall_{C \in \py} \pendsof{C}{\pn} = \{ B \}
185 \[\eqn{Tip Contents:}{
186 \bigforall_{C \in \py} D \isin C \equiv
187 { D \isin \baseof{C} \lor \atop
188 (D \in \py \land D \le C) }
190 \[\eqn{Base Acyclic:}{
191 \bigforall_{B \in \pn} D \isin B \implies D \notin \py
194 \bigforall_{C,\p} C \haspatch \p \lor C \nothaspatch \p
196 \[\eqn{Foreign Inclusion:}{
197 \bigforall_{D \text{ s.t. } \patchof{D} = \bot} D \isin C \equiv D \leq C
199 \[\eqn{Foreign Contents:}{
200 \bigforall_{C \text{ s.t. } \patchof{C} = \bot}
201 D \le C \implies \patchof{D} = \bot
204 \section{Some lemmas}
206 \[ \eqn{Alternative (overlapping) formulations defining
207 $\mergeof{C}{L}{M}{R}$:}{
210 D \isin L \equiv D \isin R : & D = C \lor D \isin L \\
211 D \isin L \nequiv D \isin R : & D = C \lor D \not\isin M \\
212 D \isin L \equiv D \isin M : & D = C \lor D \isin R \\
213 D \isin L \nequiv D \isin M : & D = C \lor D \isin L \\
214 \text{as above with L and R exchanged}
220 Original definition is symmetrical in $L$ and $R$.
223 \[ \eqn{Exclusive Tip Contents:}{
224 \bigforall_{C \in \py}
225 \neg \Bigl[ D \isin \baseof{C} \land ( D \in \py \land D \le C )
228 Ie, the two limbs of the RHS of Tip Contents are mutually exclusive.
231 Let $B = \baseof{C}$ in $D \isin \baseof{C}$. Now $B \in \pn$.
232 So by Base Acyclic $D \isin B \implies D \notin \py$.
234 \[ \eqntag{{\it Corollary - equivalent to Tip Contents}}{
235 \bigforall_{C \in \py} D \isin C \equiv
237 D \in \py : & D \le C \\
238 D \not\in \py : & D \isin \baseof{C}
242 \[ \eqn{Tip Self Inpatch:}{
243 \bigforall_{C \in \py} C \haspatch \p
245 Ie, tip commits contain their own patch.
248 Apply Exclusive Tip Contents to some $D \in \py$:
249 $ \bigforall_{C \in \py}\bigforall_{D \in \py}
250 D \isin C \equiv D \le C $
253 \[ \eqn{Exact Ancestors:}{
254 \bigforall_{ C \hasparents \set{R} }
256 ( \mathop{\hbox{\huge{$\vee$}}}_{R \in \set R} D \le R )
261 \[ \eqn{Transitive Ancestors:}{
262 \left[ \bigforall_{ E \in \pendsof{C}{\set P} } E \le M \right] \equiv
263 \left[ \bigforall_{ A \in \pancsof{C}{\set P} } A \le M \right]
267 The implication from right to left is trivial because
268 $ \pends() \subset \pancs() $.
269 For the implication from left to right:
270 by the definition of $\mathcal E$,
271 for every such $A$, either $A \in \pends()$ which implies
272 $A \le M$ by the LHS directly,
273 or $\exists_{A' \in \pancs()} \; A' \neq A \land A \le A' $
274 in which case we repeat for $A'$. Since there are finitely many
275 commits, this terminates with $A'' \in \pends()$, ie $A'' \le M$
276 by the LHS. And $A \le A''$.
279 \[ \eqn{Calculation Of Ends:}{
280 \bigforall_{C \hasparents \set A}
281 \pendsof{C}{\set P} =
285 C \not\in \p : & \displaystyle
287 \Bigl[ \Largeexists_{A \in \set A}
288 E \in \pendsof{A}{\set P} \Bigr] \land
289 \Bigl[ \Largenexists_{B \in \set A}
290 E \neq B \land E \le B \Bigr]
296 \[ \eqn{Ingredients Prevent Replay:}{
298 {C \hasparents \set A} \land
303 \Largeexists_{A \in \set A} D \isin A
305 \right] \implies \left[
306 D \isin C \implies D \le C
310 Trivial for $D = C$. Consider some $D \neq C$, $D \isin C$.
311 By the preconditions, there is some $A$ s.t. $D \in \set A$
312 and $D \isin A$. By No Replay for $A$, $D \le A$. And
313 $A \le C$ so $D \le C$.
316 \[ \eqn{Totally Foreign Contents:}{
317 \bigforall_{C \hasparents \set A}
319 \patchof{C} = \bot \land
320 \bigforall_{A \in \set A} \patchof{A} = \bot
330 Consider some $D \le C$. If $D = C$, $\patchof{D} = \bot$ trivially.
331 If $D \neq C$ then $D \le A$ where $A \in \set A$. By Foreign
332 Contents of $A$, $\patchof{D} = \bot$.
335 \section{Commit annotation}
337 We annotate each Topbloke commit $C$ with:
341 \baseof{C}, \text{ if } C \in \py
344 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
346 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
349 $\patchof{C}$, for each kind of Topbloke-generated commit, is stated
350 in the summary in the section for that kind of commit.
352 Whether $\baseof{C}$ is required, and if so what the value is, is
353 stated in the proof of Unique Base for each kind of commit.
355 $C \haspatch \pa{Q}$ or $\nothaspatch \pa{Q}$ is represented as the
356 set $\{ \pa{Q} | C \haspatch \pa{Q} \}$. Whether $C \haspatch \pa{Q}$
358 (in terms of $I \haspatch \pa{Q}$ or $I \nothaspatch \pa{Q}$
359 for the ingredients $I$),
360 in the proof of Coherence for each kind of commit.
362 $\pendsof{C}{\pa{Q}^+}$ is computed, for all Topbloke-generated commits,
363 using the lemma Calculation of Ends, above.
364 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
365 make it wrong to make plain commits with git because the recorded $\pends$
366 would have to be updated. The annotation is not needed in that case
367 because $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
369 \section{Simple commit}
371 A simple single-parent forward commit $C$ as made by git-commit.
373 \tag*{} C \hasparents \{ A \} \\
374 \tag*{} \patchof{C} = \patchof{A} \\
375 \tag*{} D \isin C \equiv D \isin A \lor D = C
377 This also covers Topbloke-generated commits on plain git branches:
378 Topbloke strips the metadata when exporting.
380 \subsection{No Replay}
382 Ingredients Prevent Replay applies. $\qed$
384 \subsection{Unique Base}
385 If $A, C \in \py$ then by Calculation of Ends for
386 $C, \py, C \not\in \py$:
387 $\pendsof{C}{\pn} = \pendsof{A}{\pn}$ so
388 $\baseof{C} = \baseof{A}$. $\qed$
390 \subsection{Tip Contents}
391 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
392 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
393 Substitute into the contents of $C$:
394 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
396 Since $D = C \implies D \in \py$,
397 and substituting in $\baseof{C}$, this gives:
398 \[ D \isin C \equiv D \isin \baseof{C} \lor
399 (D \in \py \land D \le A) \lor
400 (D = C \land D \in \py) \]
401 \[ \equiv D \isin \baseof{C} \lor
402 [ D \in \py \land ( D \le A \lor D = C ) ] \]
403 So by Exact Ancestors:
404 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
408 \subsection{Base Acyclic}
410 Need to consider only $A, C \in \pn$.
412 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
414 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
415 $A$, $D \isin C \implies D \not\in \py$.
419 \subsection{Coherence and patch inclusion}
421 Need to consider $D \in \py$
423 \subsubsection{For $A \haspatch P, D = C$:}
429 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
431 \subsubsection{For $A \haspatch P, D \neq C$:}
432 Ancestors: $ D \le C \equiv D \le A $.
434 Contents: $ D \isin C \equiv D \isin A \lor f $
435 so $ D \isin C \equiv D \isin A $.
438 \[ A \haspatch P \implies C \haspatch P \]
440 \subsubsection{For $A \nothaspatch P$:}
442 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
445 Now by contents of $A$, $D \notin A$, so $D \notin C$.
448 \[ A \nothaspatch P \implies C \nothaspatch P \]
451 \subsection{Foreign inclusion:}
453 If $D = C$, trivial. For $D \neq C$:
454 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
456 \subsection{Foreign Contents:}
458 Only relevant if $\patchof{C} = \bot$, and in that case Totally
459 Foreign Contents applies. $\qed$
461 \section{Create Base}
463 Given $L$, create a Topbloke base branch initial commit $B$.
465 B \hasparents \{ L \}
467 \patchof{B} = \pan{Q}
469 D \isin B \equiv D \isin L \lor D = B
472 \subsection{Conditions}
474 \[ \eqn{ Ingredients }{
475 \patchof{L} = \pa{L} \lor \patchof{L} = \bot
477 \[ \eqn{ Non-recursion }{
481 \subsection{No Replay}
483 Ingredients Prevent Replay applies. $\qed$
485 \subsection{Unique Base}
489 \subsection{Tip Contents}
493 \subsection{Base Acyclic}
495 Consider some $D \isin B$. If $D = B$, $D \in \pn$, OK.
497 If $D \neq B$, $D \isin L$. By No Replay of $D$ in $L$, $D \le L$.
498 Thus by Foreign Contents of $L$, $\patchof{D} = \bot$. OK.
504 \subsection{Coherence and Patch Inclusion}
506 Consider some $D \in \p$.
507 $B \not\in \py$ so $D \neq B$. So $D \isin B \equiv D \isin L$.
509 Thus $L \haspatch \p \implies B \haspatch P$
510 and $L \nothaspatch \p \implies B \nothaspatch P$.
514 \subsection{Foreign Inclusion}
516 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq B$
517 so $D \isin B \equiv D \isin L$.
518 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
519 And by Exact Ancestors $D \le L \equiv D \le B$.
520 So $D \isin B \equiv D \le B$. $\qed$
522 \subsection{Foreign Contents}
528 Given a Topbloke base $B$, create a tip branch initial commit B.
530 C \hasparents \{ B \}
532 \patchof{B} = \pay{Q}
534 D \isin C \equiv D \isin B \lor D = C
537 \subsection{Conditions}
539 \[ \eqn{ Ingredients }{
540 \patchof{B} = \pan{Q}
543 \subsection{No Replay}
545 Ingredients Prevent Replay applies. $\qed$
547 \subsection{Unique Base}
549 Trivially, $\pendsof{C}{\pan{Q}} = \{B\}$ so $\baseof{C} = B$.
551 \subsection{Tip Contents}
553 Consider some arbitrary commit $D$. If $D = C$, trivially satisfied.
555 If $D \neq C$, $D \isin C \equiv D \isin B$.
556 By Base Acyclic of $B$, $D \isin B \implies D \not\in \pay{Q}$.
557 So $D \isin C \equiv D \isin \baseof{B}$.
565 Given $L$ and $\pr$ as represented by $R^+, R^-$.
566 Construct $C$ which has $\pr$ removed.
567 Used for removing a branch dependency.
569 C \hasparents \{ L \}
571 \patchof{C} = \patchof{L}
573 \mergeof{C}{L}{R^+}{R^-}
576 \subsection{Conditions}
578 \[ \eqn{ Ingredients }{
579 R^+ \in \pry \land R^- = \baseof{R^+}
581 \[ \eqn{ Into Base }{
584 \[ \eqn{ Unique Tip }{
585 \pendsof{L}{\pry} = \{ R^+ \}
587 \[ \eqn{ Currently Included }{
591 \subsection{Ordering of Ingredients:}
593 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
594 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
597 (Note that $R^+ \not\le R^-$, i.e. the merge base
598 is a descendant, not an ancestor, of the 2nd parent.)
600 \subsection{No Replay}
602 By definition of $\merge$,
603 $D \isin C \implies D \isin L \lor D \isin R^- \lor D = C$.
604 So, by Ordering of Ingredients,
605 Ingredients Prevent Replay applies. $\qed$
607 \subsection{Desired Contents}
609 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
612 \subsubsection{For $D = C$:}
614 Trivially $D \isin C$. OK.
616 \subsubsection{For $D \neq C, D \not\le L$:}
618 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
619 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
621 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
623 By Currently Included, $D \isin L$.
625 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
626 by Unique Tip, $D \le R^+ \equiv D \le L$.
629 By Base Acyclic, $D \not\isin R^-$.
631 Apply $\merge$: $D \not\isin C$. OK.
633 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
635 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
637 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
641 \subsection{Unique Base}
643 Into Base means that $C \in \pn$, so Unique Base is not
646 \subsection{Tip Contents}
648 Again, not applicable. $\qed$
650 \subsection{Base Acyclic}
652 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
653 And by Into Base $C \not\in \py$.
654 Now from Desired Contents, above, $D \isin C
655 \implies D \isin L \lor D = C$, which thus
656 $\implies D \not\in \py$. $\qed$.
658 \subsection{Coherence and Patch Inclusion}
660 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
662 \subsubsection{For $\p = \pr$:}
663 By Desired Contents, above, $D \not\isin C$.
664 So $C \nothaspatch \pr$.
666 \subsubsection{For $\p \neq \pr$:}
667 By Desired Contents, $D \isin C \equiv D \isin L$
668 (since $D \in \py$ so $D \not\in \pry$).
670 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
671 So $L \nothaspatch \p \implies C \nothaspatch \p$.
673 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
674 so $L \haspatch \p \implies C \haspatch \p$.
678 \subsection{Foreign Inclusion}
680 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
681 So by Desired Contents $D \isin C \equiv D \isin L$.
682 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
684 And $D \le C \equiv D \le L$.
685 Thus $D \isin C \equiv D \le C$.
689 \subsection{Foreign Contents}
695 Merge commits $L$ and $R$ using merge base $M$:
697 C \hasparents \{ L, R \}
699 \patchof{C} = \patchof{L}
703 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
705 \subsection{Conditions}
706 \[ \eqn{ Ingredients }{
709 \[ \eqn{ Tip Merge }{
712 R \in \py : & \baseof{R} \ge \baseof{L}
713 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
714 R \in \pn : & M = \baseof{L} \\
715 \text{otherwise} : & \false
718 \[ \eqn{ Merge Acyclic }{
723 \[ \eqn{ Removal Merge Ends }{
724 X \not\haspatch \p \land
728 \pendsof{Y}{\py} = \pendsof{M}{\py}
730 \[ \eqn{ Addition Merge Ends }{
731 X \not\haspatch \p \land
735 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
738 \[ \eqn{ Foreign Merges }{
739 \patchof{L} = \bot \equiv \patchof{R} = \bot
742 \subsection{Non-Topbloke merges}
744 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$
745 (Foreign Merges, above).
746 I.e. not only is it forbidden to merge into a Topbloke-controlled
747 branch without Topbloke's assistance, it is also forbidden to
748 merge any Topbloke-controlled branch into any plain git branch.
750 Given those conditions, Tip Merge and Merge Acyclic do not apply.
751 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
752 Merge Ends condition applies.
754 So a plain git merge of non-Topbloke branches meets the conditions and
755 is therefore consistent with our scheme.
757 \subsection{No Replay}
759 By definition of $\merge$,
760 $D \isin C \implies D \isin L \lor D \isin R \lor D = C$.
762 Ingredients Prevent Replay applies. $\qed$
764 \subsection{Unique Base}
766 Need to consider only $C \in \py$, ie $L \in \py$,
767 and calculate $\pendsof{C}{\pn}$. So we will consider some
768 putative ancestor $A \in \pn$ and see whether $A \le C$.
770 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
771 But $C \in py$ and $A \in \pn$ so $A \neq C$.
772 Thus $A \le C \equiv A \le L \lor A \le R$.
774 By Unique Base of L and Transitive Ancestors,
775 $A \le L \equiv A \le \baseof{L}$.
777 \subsubsection{For $R \in \py$:}
779 By Unique Base of $R$ and Transitive Ancestors,
780 $A \le R \equiv A \le \baseof{R}$.
782 But by Tip Merge condition on $\baseof{R}$,
783 $A \le \baseof{L} \implies A \le \baseof{R}$, so
784 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
785 Thus $A \le C \equiv A \le \baseof{R}$.
786 That is, $\baseof{C} = \baseof{R}$.
788 \subsubsection{For $R \in \pn$:}
790 By Tip Merge condition on $R$ and since $M \le R$,
791 $A \le \baseof{L} \implies A \le R$, so
792 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
793 Thus $A \le C \equiv A \le R$.
794 That is, $\baseof{C} = R$.
798 \subsection{Coherence and Patch Inclusion}
800 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
801 This involves considering $D \in \py$.
803 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
804 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
805 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
806 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
808 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
809 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
810 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
812 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
814 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
815 \equiv D \isin L \lor D \isin R$.
816 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
818 Consider $D \neq C, D \isin X \land D \isin Y$:
819 By $\merge$, $D \isin C$. Also $D \le X$
820 so $D \le C$. OK for $C \haspatch \p$.
822 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
823 By $\merge$, $D \not\isin C$.
824 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
825 OK for $C \haspatch \p$.
827 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
828 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
829 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
830 OK for $C \haspatch \p$.
832 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
834 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
836 $M \haspatch \p \implies C \nothaspatch \p$.
837 $M \nothaspatch \p \implies C \haspatch \p$.
841 One of the Merge Ends conditions applies.
842 Recall that we are considering $D \in \py$.
843 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
844 We will show for each of
845 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
846 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
848 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
849 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
850 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
851 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
853 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
854 $D \le Y$ so $D \le C$.
855 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
857 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
858 $D \not\le Y$. If $D \le X$ then
859 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
860 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
861 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
863 Consider $D \neq C, M \haspatch P, D \isin Y$:
864 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
865 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
866 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
868 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
869 By $\merge$, $D \not\isin C$. OK.
873 \subsection{Base Acyclic}
875 This applies when $C \in \pn$.
876 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
878 Consider some $D \in \py$.
880 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
881 R$. And $D \neq C$. So $D \not\isin C$.
885 \subsection{Tip Contents}
887 We need worry only about $C \in \py$.
888 And $\patchof{C} = \patchof{L}$
889 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
890 of $C$, and its Coherence and Patch Inclusion, as just proved.
892 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
893 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
894 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
895 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
896 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
898 We will consider an arbitrary commit $D$
899 and prove the Exclusive Tip Contents form.
901 \subsubsection{For $D \in \py$:}
902 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
905 \subsubsection{For $D \not\in \py, R \not\in \py$:}
907 $D \neq C$. By Tip Contents of $L$,
908 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
909 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
910 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
911 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
913 \subsubsection{For $D \not\in \py, R \in \py$:}
918 $D \isin L \equiv D \isin \baseof{L}$ and
919 $D \isin R \equiv D \isin \baseof{R}$.
921 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
922 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
923 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
924 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
926 So $D \isin M \equiv D \isin L$ and by $\merge$,
927 $D \isin C \equiv D \isin R$. But from Unique Base,
928 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
932 \subsection{Foreign Inclusion}
934 Consider some $D$ s.t. $\patchof{D} = \bot$.
935 By Foreign Inclusion of $L, M, R$:
936 $D \isin L \equiv D \le L$;
937 $D \isin M \equiv D \le M$;
938 $D \isin R \equiv D \le R$.
940 \subsubsection{For $D = C$:}
942 $D \isin C$ and $D \le C$. OK.
944 \subsubsection{For $D \neq C, D \isin M$:}
946 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
947 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
949 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
951 By $\merge$, $D \isin C$.
952 And $D \isin X$ means $D \le X$ so $D \le C$.
955 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
957 By $\merge$, $D \not\isin C$.
958 And $D \not\le L, D \not\le R$ so $D \not\le C$.
963 \subsection{Foreign Contents}
965 Only relevant if $\patchof{L} = \bot$, in which case
966 $\patchof{C} = \bot$ and by Foreign Merges $\patchof{R} = \bot$,
967 so Totally Foreign Contents applies. $\qed$