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 )
256 \[ \eqn{Transitive Ancestors:}{
257 \left[ \bigforall_{ E \in \pendsof{C}{\set P} } E \le M \right] \equiv
258 \left[ \bigforall_{ A \in \pancsof{C}{\set P} } A \le M \right]
262 The implication from right to left is trivial because
263 $ \pends() \subset \pancs() $.
264 For the implication from left to right:
265 by the definition of $\mathcal E$,
266 for every such $A$, either $A \in \pends()$ which implies
267 $A \le M$ by the LHS directly,
268 or $\exists_{A' \in \pancs()} \; A' \neq A \land A \le A' $
269 in which case we repeat for $A'$. Since there are finitely many
270 commits, this terminates with $A'' \in \pends()$, ie $A'' \le M$
271 by the LHS. And $A \le A''$.
273 \[ \eqn{Calculation Of Ends:}{
274 \bigforall_{C \hasparents \set A}
275 \pendsof{C}{\set P} =
277 \Bigl[ \Largeexists_{A \in \set A}
278 E \in \pendsof{A}{\set P} \Bigr] \land
279 \Bigl[ \Largenexists_{B \in \set A}
280 E \neq B \land E \le B \Bigr]
285 \subsection{No Replay for Merge Results}
287 If we are constructing $C$, with,
295 No Replay is preserved. \proofstarts
297 \subsubsection{For $D=C$:} $D \isin C, D \le C$. OK.
299 \subsubsection{For $D \isin L \land D \isin R$:}
300 $D \isin C$. And $D \isin L \implies D \le L \implies D \le C$. OK.
302 \subsubsection{For $D \neq C \land D \not\isin L \land D \not\isin R$:}
305 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
306 \land D \not\isin M$:}
307 $D \isin C$. Also $D \isin L \lor D \isin R$ so $D \le L \lor D \le
310 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
316 \section{Commit annotation}
318 We annotate each Topbloke commit $C$ with:
322 \baseof{C}, \text{ if } C \in \py
325 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
327 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
330 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
331 make it wrong to make plain commits with git because the recorded $\pends$
332 would have to be updated. The annotation is not needed because
333 $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
335 \section{Simple commit}
337 A simple single-parent forward commit $C$ as made by git-commit.
339 \tag*{} C \hasparents \{ A \} \\
340 \tag*{} \patchof{C} = \patchof{A} \\
341 \tag*{} D \isin C \equiv D \isin A \lor D = C
343 This also covers Topbloke-generated commits on plain git branches:
344 Topbloke strips the metadata when exporting.
346 \subsection{No Replay}
349 \subsection{Unique Base}
350 If $A, C \in \py$ then $\baseof{C} = \baseof{A}$. $\qed$
352 \subsection{Tip Contents}
353 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
354 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
355 Substitute into the contents of $C$:
356 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
358 Since $D = C \implies D \in \py$,
359 and substituting in $\baseof{C}$, this gives:
360 \[ D \isin C \equiv D \isin \baseof{C} \lor
361 (D \in \py \land D \le A) \lor
362 (D = C \land D \in \py) \]
363 \[ \equiv D \isin \baseof{C} \lor
364 [ D \in \py \land ( D \le A \lor D = C ) ] \]
365 So by Exact Ancestors:
366 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
370 \subsection{Base Acyclic}
372 Need to consider only $A, C \in \pn$.
374 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
376 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
377 $A$, $D \isin C \implies D \not\in \py$. $\qed$
379 \subsection{Coherence and patch inclusion}
381 Need to consider $D \in \py$
383 \subsubsection{For $A \haspatch P, D = C$:}
389 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
391 \subsubsection{For $A \haspatch P, D \neq C$:}
392 Ancestors: $ D \le C \equiv D \le A $.
394 Contents: $ D \isin C \equiv D \isin A \lor f $
395 so $ D \isin C \equiv D \isin A $.
398 \[ A \haspatch P \implies C \haspatch P \]
400 \subsubsection{For $A \nothaspatch P$:}
402 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
405 Now by contents of $A$, $D \notin A$, so $D \notin C$.
408 \[ A \nothaspatch P \implies C \nothaspatch P \]
411 \subsection{Foreign inclusion:}
413 If $D = C$, trivial. For $D \neq C$:
414 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
418 Given $L, R^+, R^-$ where
419 $R^+ \in \pry, R^- = \baseof{R^+}$.
420 Construct $C$ which has $\pr$ removed.
421 Used for removing a branch dependency.
423 C \hasparents \{ L \}
425 \patchof{C} = \patchof{L}
427 \mergeof{C}{L}{R^+}{R^-}
430 \subsection{Conditions}
432 \[ \eqn{ Into Base }{
435 \[ \eqn{ Unique Tip }{
436 \pendsof{L}{\pry} = \{ R^+ \}
438 \[ \eqn{ Currently Included }{
442 \subsection{No Replay}
444 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
445 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$ and No Replay for
446 Merge Results applies. $\qed$
448 \subsection{Desired Contents}
450 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
453 \subsubsection{For $D = C$:}
455 Trivially $D \isin C$. OK.
457 \subsubsection{For $D \neq C, D \not\le L$:}
459 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
460 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
462 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
464 By Currently Included, $D \isin L$.
466 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
467 by Unique Tip, $D \le R^+ \equiv D \le L$.
470 By Base Acyclic, $D \not\isin R^-$.
472 Apply $\merge$: $D \not\isin C$. OK.
474 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
476 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
478 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
482 \subsection{Unique Base}
484 Into Base means that $C \in \pn$, so Unique Base is not
487 \subsection{Tip Contents}
489 Again, not applicable. $\qed$
491 \subsection{Base Acyclic}
493 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
494 And by Into Base $C \not\in \py$.
495 Now from Desired Contents, above, $D \isin C
496 \implies D \isin L \lor D = C$, which thus
497 $\implies D \not\in \py$. $\qed$.
501 Merge commits $L$ and $R$ using merge base $M$ ($M < L, M < R$):
503 C \hasparents \{ L, R \}
505 \patchof{C} = \patchof{L}
509 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
511 \subsection{Conditions}
513 \[ \eqn{ Tip Merge }{
516 R \in \py : & \baseof{R} \ge \baseof{L}
517 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
518 R \in \pn : & M = \baseof{L} \\
519 \text{otherwise} : & \false
522 \[ \eqn{ Merge Acyclic }{
527 \[ \eqn{ Removal Merge Ends }{
528 X \not\haspatch \p \land
532 \pendsof{Y}{\py} = \pendsof{M}{\py}
534 \[ \eqn{ Addition Merge Ends }{
535 X \not\haspatch \p \land
539 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
543 \subsection{Non-Topbloke merges}
545 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$.
546 I.e. not only is it forbidden to merge into a Topbloke-controlled
547 branch without Topbloke's assistance, it is also forbidden to
548 merge any Topbloke-controlled branch into any plain git branch.
550 Given those conditions, Tip Merge and Merge Acyclic do not apply.
551 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
552 Merge Ends condition applies. Good.
554 \subsection{No Replay}
556 See No Replay for Merge Results.
558 \subsection{Unique Base}
560 Need to consider only $C \in \py$, ie $L \in \py$,
561 and calculate $\pendsof{C}{\pn}$. So we will consider some
562 putative ancestor $A \in \pn$ and see whether $A \le C$.
564 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
565 But $C \in py$ and $A \in \pn$ so $A \neq C$.
566 Thus $A \le C \equiv A \le L \lor A \le R$.
568 By Unique Base of L and Transitive Ancestors,
569 $A \le L \equiv A \le \baseof{L}$.
571 \subsubsection{For $R \in \py$:}
573 By Unique Base of $R$ and Transitive Ancestors,
574 $A \le R \equiv A \le \baseof{R}$.
576 But by Tip Merge condition on $\baseof{R}$,
577 $A \le \baseof{L} \implies A \le \baseof{R}$, so
578 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
579 Thus $A \le C \equiv A \le \baseof{R}$.
580 That is, $\baseof{C} = \baseof{R}$.
582 \subsubsection{For $R \in \pn$:}
584 By Tip Merge condition on $R$ and since $M \le R$,
585 $A \le \baseof{L} \implies A \le R$, so
586 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
587 Thus $A \le C \equiv A \le R$.
588 That is, $\baseof{C} = R$.
592 \subsection{Coherence and Patch Inclusion}
594 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
595 This involves considering $D \in \py$.
597 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
598 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
599 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
600 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
602 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
603 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
604 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
606 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
608 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
609 \equiv D \isin L \lor D \isin R$.
610 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
612 Consider $D \neq C, D \isin X \land D \isin Y$:
613 By $\merge$, $D \isin C$. Also $D \le X$
614 so $D \le C$. OK for $C \haspatch \p$.
616 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
617 By $\merge$, $D \not\isin C$.
618 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
619 OK for $C \haspatch \p$.
621 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
622 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
623 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
624 OK for $C \haspatch \p$.
626 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
628 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
630 $C \haspatch \p \equiv M \nothaspatch \p$.
634 One of the Merge Ends conditions applies.
635 Recall that we are considering $D \in \py$.
636 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
637 We will show for each of
638 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
639 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
641 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
642 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
643 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
644 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
646 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
647 $D \le Y$ so $D \le C$.
648 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
650 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
651 $D \not\le Y$. If $D \le X$ then
652 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
653 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
654 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
656 Consider $D \neq C, M \haspatch P, D \isin Y$:
657 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
658 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
659 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
661 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
662 By $\merge$, $D \not\isin C$. OK.
666 \subsection{Base Acyclic}
668 This applies when $C \in \pn$.
669 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
671 Consider some $D \in \py$.
673 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
674 R$. And $D \neq C$. So $D \not\isin C$. $\qed$
676 \subsection{Tip Contents}
678 We need worry only about $C \in \py$.
679 And $\patchof{C} = \patchof{L}$
680 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
681 of $C$, and its Coherence and Patch Inclusion, as just proved.
683 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
684 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
685 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
686 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
687 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
689 We will consider an arbitrary commit $D$
690 and prove the Exclusive Tip Contents form.
692 \subsubsection{For $D \in \py$:}
693 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
696 \subsubsection{For $D \not\in \py, R \not\in \py$:}
698 $D \neq C$. By Tip Contents of $L$,
699 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
700 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
701 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
702 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
704 \subsubsection{For $D \not\in \py, R \in \py$:}
709 $D \isin L \equiv D \isin \baseof{L}$ and
710 $D \isin R \equiv D \isin \baseof{R}$.
712 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
713 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
714 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
715 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
717 So $D \isin M \equiv D \isin L$ and by $\merge$,
718 $D \isin C \equiv D \isin R$. But from Unique Base,
719 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
723 \subsection{Foreign Inclusion}
725 Consider some $D$ s.t. $\patchof{D} = \bot$.
726 By Foreign Inclusion of $L, M, R$:
727 $D \isin L \equiv D \le L$;
728 $D \isin M \equiv D \le M$;
729 $D \isin R \equiv D \le R$.
731 \subsubsection{For $D = C$:}
733 $D \isin C$ and $D \le C$. OK.
735 \subsubsection{For $D \neq C, D \isin M$:}
737 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
738 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
740 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
742 By $\merge$, $D \isin C$.
743 And $D \isin X$ means $D \le X$ so $D \le C$.
746 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
748 By $\merge$, $D \not\isin C$.
749 And $D \not\le L, D \not\le R$ so $D \not\le C$.