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
200 \section{Some lemmas}
202 \[ \eqn{Alternative (overlapping) formulations defining
203 $\mergeof{C}{L}{M}{R}$:}{
206 D \isin L \equiv D \isin R : & D = C \lor D \isin L \\
207 D \isin L \nequiv D \isin R : & D = C \lor D \not\isin M \\
208 D \isin L \equiv D \isin M : & D = C \lor D \isin R \\
209 D \isin L \nequiv D \isin M : & D = C \lor D \isin L \\
210 \text{as above with L and R exchanged}
216 Original definition is symmetrical in $L$ and $R$.
219 \[ \eqn{Exclusive Tip Contents:}{
220 \bigforall_{C \in \py}
221 \neg \Bigl[ D \isin \baseof{C} \land ( D \in \py \land D \le C )
224 Ie, the two limbs of the RHS of Tip Contents are mutually exclusive.
227 Let $B = \baseof{C}$ in $D \isin \baseof{C}$. Now $B \in \pn$.
228 So by Base Acyclic $D \isin B \implies D \notin \py$.
230 \[ \eqntag{{\it Corollary - equivalent to Tip Contents}}{
231 \bigforall_{C \in \py} D \isin C \equiv
233 D \in \py : & D \le C \\
234 D \not\in \py : & D \isin \baseof{C}
238 \[ \eqn{Tip Self Inpatch:}{
239 \bigforall_{C \in \py} C \haspatch \p
241 Ie, tip commits contain their own patch.
244 Apply Exclusive Tip Contents to some $D \in \py$:
245 $ \bigforall_{C \in \py}\bigforall_{D \in \py}
246 D \isin C \equiv D \le C $
249 \[ \eqn{Exact Ancestors:}{
250 \bigforall_{ C \hasparents \set{R} }
252 ( \mathop{\hbox{\huge{$\vee$}}}_{R \in \set R} D \le R )
257 \[ \eqn{Transitive Ancestors:}{
258 \left[ \bigforall_{ E \in \pendsof{C}{\set P} } E \le M \right] \equiv
259 \left[ \bigforall_{ A \in \pancsof{C}{\set P} } A \le M \right]
263 The implication from right to left is trivial because
264 $ \pends() \subset \pancs() $.
265 For the implication from left to right:
266 by the definition of $\mathcal E$,
267 for every such $A$, either $A \in \pends()$ which implies
268 $A \le M$ by the LHS directly,
269 or $\exists_{A' \in \pancs()} \; A' \neq A \land A \le A' $
270 in which case we repeat for $A'$. Since there are finitely many
271 commits, this terminates with $A'' \in \pends()$, ie $A'' \le M$
272 by the LHS. And $A \le A''$.
275 \[ \eqn{Calculation Of Ends:}{
276 \bigforall_{C \hasparents \set A}
277 \pendsof{C}{\set P} =
281 C \not\in \p : & \displaystyle
283 \Bigl[ \Largeexists_{A \in \set A}
284 E \in \pendsof{A}{\set P} \Bigr] \land
285 \Bigl[ \Largenexists_{B \in \set A}
286 E \neq B \land E \le B \Bigr]
292 \subsection{No Replay for Merge Results}
294 If we are constructing $C$, with,
302 No Replay is preserved. \proofstarts
304 \subsubsection{For $D=C$:} $D \isin C, D \le C$. OK.
306 \subsubsection{For $D \isin L \land D \isin R$:}
307 $D \isin C$. And $D \isin L \implies D \le L \implies D \le C$. OK.
309 \subsubsection{For $D \neq C \land D \not\isin L \land D \not\isin R$:}
312 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
313 \land D \not\isin M$:}
314 $D \isin C$. Also $D \isin L \lor D \isin R$ so $D \le L \lor D \le
317 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
323 \section{Commit annotation}
325 We annotate each Topbloke commit $C$ with:
329 \baseof{C}, \text{ if } C \in \py
332 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
334 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
337 $\patchof{C}$, for each kind of Topbloke-generated commit, is stated
338 in the summary in the section for that kind of commit.
340 Whether $\baseof{C}$ is required, and if so what the value is, is
341 stated in the proof of Unique Base for each kind of commit.
343 $C \haspatch \pa{Q}$ or $\nothaspatch \pa{Q}$ is represented as the
344 set $\{ \pa{Q} | C \haspatch \pa{Q} \}$. Whether $C \haspatch \pa{Q}$
346 (in terms of $I \haspatch \pa{Q}$ or $I \nothaspatch \pa{Q}$
347 for the ingredients $I$),
348 in the proof of Coherence for each kind of commit.
350 $\pendsof{C}{\pa{Q}^+}$ is computed, for all Topbloke-generated commits,
351 using the lemma Calculation of Ends, above.
352 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
353 make it wrong to make plain commits with git because the recorded $\pends$
354 would have to be updated. The annotation is not needed in that case
355 because $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
357 \section{Simple commit}
359 A simple single-parent forward commit $C$ as made by git-commit.
361 \tag*{} C \hasparents \{ A \} \\
362 \tag*{} \patchof{C} = \patchof{A} \\
363 \tag*{} D \isin C \equiv D \isin A \lor D = C
365 This also covers Topbloke-generated commits on plain git branches:
366 Topbloke strips the metadata when exporting.
368 \subsection{No Replay}
371 \subsection{Unique Base}
372 If $A, C \in \py$ then by Calculation of Ends for
373 $C, \py, C \not\in \py$:
374 $\pendsof{C}{\pn} = \pendsof{A}{\pn}$ so
375 $\baseof{C} = \baseof{A}$. $\qed$
377 \subsection{Tip Contents}
378 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
379 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
380 Substitute into the contents of $C$:
381 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
383 Since $D = C \implies D \in \py$,
384 and substituting in $\baseof{C}$, this gives:
385 \[ D \isin C \equiv D \isin \baseof{C} \lor
386 (D \in \py \land D \le A) \lor
387 (D = C \land D \in \py) \]
388 \[ \equiv D \isin \baseof{C} \lor
389 [ D \in \py \land ( D \le A \lor D = C ) ] \]
390 So by Exact Ancestors:
391 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
395 \subsection{Base Acyclic}
397 Need to consider only $A, C \in \pn$.
399 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
401 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
402 $A$, $D \isin C \implies D \not\in \py$. $\qed$
404 \subsection{Coherence and patch inclusion}
406 Need to consider $D \in \py$
408 \subsubsection{For $A \haspatch P, D = C$:}
414 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
416 \subsubsection{For $A \haspatch P, D \neq C$:}
417 Ancestors: $ D \le C \equiv D \le A $.
419 Contents: $ D \isin C \equiv D \isin A \lor f $
420 so $ D \isin C \equiv D \isin A $.
423 \[ A \haspatch P \implies C \haspatch P \]
425 \subsubsection{For $A \nothaspatch P$:}
427 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
430 Now by contents of $A$, $D \notin A$, so $D \notin C$.
433 \[ A \nothaspatch P \implies C \nothaspatch P \]
436 \subsection{Foreign inclusion:}
438 If $D = C$, trivial. For $D \neq C$:
439 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
443 Given $L, R^+, R^-$ where
444 $R^+ \in \pry, R^- = \baseof{R^+}$.
445 Construct $C$ which has $\pr$ removed.
446 Used for removing a branch dependency.
448 C \hasparents \{ L \}
450 \patchof{C} = \patchof{L}
452 \mergeof{C}{L}{R^+}{R^-}
455 \subsection{Conditions}
457 \[ \eqn{ Into Base }{
460 \[ \eqn{ Unique Tip }{
461 \pendsof{L}{\pry} = \{ R^+ \}
463 \[ \eqn{ Currently Included }{
467 \subsection{Ordering of ${L, R^+, R^-}$:}
469 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
470 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
472 (Note that the merge base $R^+ \not\le R^-$, i.e. the merge base is
473 later than one of the branches to be merged.)
475 \subsection{No Replay}
477 No Replay for Merge Results applies. $\qed$
479 \subsection{Desired Contents}
481 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
484 \subsubsection{For $D = C$:}
486 Trivially $D \isin C$. OK.
488 \subsubsection{For $D \neq C, D \not\le L$:}
490 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
491 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
493 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
495 By Currently Included, $D \isin L$.
497 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
498 by Unique Tip, $D \le R^+ \equiv D \le L$.
501 By Base Acyclic, $D \not\isin R^-$.
503 Apply $\merge$: $D \not\isin C$. OK.
505 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
507 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
509 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
513 \subsection{Unique Base}
515 Into Base means that $C \in \pn$, so Unique Base is not
518 \subsection{Tip Contents}
520 Again, not applicable. $\qed$
522 \subsection{Base Acyclic}
524 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
525 And by Into Base $C \not\in \py$.
526 Now from Desired Contents, above, $D \isin C
527 \implies D \isin L \lor D = C$, which thus
528 $\implies D \not\in \py$. $\qed$.
530 \subsection{Coherence and Patch Inclusion}
532 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
534 \subsubsection{For $\p = \pr$:}
535 By Desired Contents, above, $D \not\isin C$.
536 So $C \nothaspatch \pr$.
538 \subsubsection{For $\p \neq \pr$:}
539 By Desired Contents, $D \isin C \equiv D \isin L$
540 (since $D \in \py$ so $D \not\in \pry$).
542 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
543 So $L \nothaspatch \p \implies C \nothaspatch \p$.
545 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
546 so $L \haspatch \p \implies C \haspatch \p$.
548 \section{Foreign Inclusion}
550 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
551 So by Desired Contents $D \isin C \equiv D \isin L$.
552 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
554 And $D \le C \equiv D \le L$.
555 Thus $D \isin C \equiv D \le C$. $\qed$
559 Merge commits $L$ and $R$ using merge base $M$ ($M < L, M < R$):
561 C \hasparents \{ L, R \}
563 \patchof{C} = \patchof{L}
567 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
569 \subsection{Conditions}
571 \[ \eqn{ Tip Merge }{
574 R \in \py : & \baseof{R} \ge \baseof{L}
575 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
576 R \in \pn : & M = \baseof{L} \\
577 \text{otherwise} : & \false
580 \[ \eqn{ Merge Acyclic }{
585 \[ \eqn{ Removal Merge Ends }{
586 X \not\haspatch \p \land
590 \pendsof{Y}{\py} = \pendsof{M}{\py}
592 \[ \eqn{ Addition Merge Ends }{
593 X \not\haspatch \p \land
597 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
601 \subsection{Non-Topbloke merges}
603 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$.
604 I.e. not only is it forbidden to merge into a Topbloke-controlled
605 branch without Topbloke's assistance, it is also forbidden to
606 merge any Topbloke-controlled branch into any plain git branch.
608 Given those conditions, Tip Merge and Merge Acyclic do not apply.
609 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
610 Merge Ends condition applies. Good.
612 \subsection{No Replay}
614 No Replay for Merge Results applies. $\qed$
616 \subsection{Unique Base}
618 Need to consider only $C \in \py$, ie $L \in \py$,
619 and calculate $\pendsof{C}{\pn}$. So we will consider some
620 putative ancestor $A \in \pn$ and see whether $A \le C$.
622 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
623 But $C \in py$ and $A \in \pn$ so $A \neq C$.
624 Thus $A \le C \equiv A \le L \lor A \le R$.
626 By Unique Base of L and Transitive Ancestors,
627 $A \le L \equiv A \le \baseof{L}$.
629 \subsubsection{For $R \in \py$:}
631 By Unique Base of $R$ and Transitive Ancestors,
632 $A \le R \equiv A \le \baseof{R}$.
634 But by Tip Merge condition on $\baseof{R}$,
635 $A \le \baseof{L} \implies A \le \baseof{R}$, so
636 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
637 Thus $A \le C \equiv A \le \baseof{R}$.
638 That is, $\baseof{C} = \baseof{R}$.
640 \subsubsection{For $R \in \pn$:}
642 By Tip Merge condition on $R$ and since $M \le R$,
643 $A \le \baseof{L} \implies A \le R$, so
644 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
645 Thus $A \le C \equiv A \le R$.
646 That is, $\baseof{C} = R$.
650 \subsection{Coherence and Patch Inclusion}
652 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
653 This involves considering $D \in \py$.
655 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
656 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
657 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
658 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
660 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
661 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
662 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
664 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
666 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
667 \equiv D \isin L \lor D \isin R$.
668 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
670 Consider $D \neq C, D \isin X \land D \isin Y$:
671 By $\merge$, $D \isin C$. Also $D \le X$
672 so $D \le C$. OK for $C \haspatch \p$.
674 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
675 By $\merge$, $D \not\isin C$.
676 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
677 OK for $C \haspatch \p$.
679 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
680 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
681 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
682 OK for $C \haspatch \p$.
684 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
686 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
688 $M \haspatch \p \implies C \nothaspatch \p$.
689 $M \nothaspatch \p \implies C \haspatch \p$.
693 One of the Merge Ends conditions applies.
694 Recall that we are considering $D \in \py$.
695 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
696 We will show for each of
697 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
698 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
700 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
701 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
702 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
703 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
705 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
706 $D \le Y$ so $D \le C$.
707 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
709 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
710 $D \not\le Y$. If $D \le X$ then
711 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
712 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
713 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
715 Consider $D \neq C, M \haspatch P, D \isin Y$:
716 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
717 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
718 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
720 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
721 By $\merge$, $D \not\isin C$. OK.
725 \subsection{Base Acyclic}
727 This applies when $C \in \pn$.
728 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
730 Consider some $D \in \py$.
732 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
733 R$. And $D \neq C$. So $D \not\isin C$. $\qed$
735 \subsection{Tip Contents}
737 We need worry only about $C \in \py$.
738 And $\patchof{C} = \patchof{L}$
739 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
740 of $C$, and its Coherence and Patch Inclusion, as just proved.
742 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
743 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
744 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
745 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
746 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
748 We will consider an arbitrary commit $D$
749 and prove the Exclusive Tip Contents form.
751 \subsubsection{For $D \in \py$:}
752 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
755 \subsubsection{For $D \not\in \py, R \not\in \py$:}
757 $D \neq C$. By Tip Contents of $L$,
758 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
759 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
760 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
761 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
763 \subsubsection{For $D \not\in \py, R \in \py$:}
768 $D \isin L \equiv D \isin \baseof{L}$ and
769 $D \isin R \equiv D \isin \baseof{R}$.
771 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
772 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
773 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
774 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
776 So $D \isin M \equiv D \isin L$ and by $\merge$,
777 $D \isin C \equiv D \isin R$. But from Unique Base,
778 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
782 \subsection{Foreign Inclusion}
784 Consider some $D$ s.t. $\patchof{D} = \bot$.
785 By Foreign Inclusion of $L, M, R$:
786 $D \isin L \equiv D \le L$;
787 $D \isin M \equiv D \le M$;
788 $D \isin R \equiv D \le R$.
790 \subsubsection{For $D = C$:}
792 $D \isin C$ and $D \le C$. OK.
794 \subsubsection{For $D \neq C, D \isin M$:}
796 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
797 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
799 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
801 By $\merge$, $D \isin C$.
802 And $D \isin X$ means $D \le X$ so $D \le C$.
805 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
807 By $\merge$, $D \not\isin C$.
808 And $D \not\le L, D \not\le R$ so $D \not\le C$.