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{Totally Foreign Contents:}{
297 \bigforall_{C \hasparents \set A}
299 \patchof{C} = \bot \land
300 \bigforall_{A \in \set A} \patchof{A} = \bot
311 \subsection{No Replay for Merge Results}
313 If we are constructing $C$, with,
321 No Replay is preserved. \proofstarts
323 \subsubsection{For $D=C$:} $D \isin C, D \le C$. OK.
325 \subsubsection{For $D \isin L \land D \isin R$:}
326 $D \isin C$. And $D \isin L \implies D \le L \implies D \le C$. OK.
328 \subsubsection{For $D \neq C \land D \not\isin L \land D \not\isin R$:}
331 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
332 \land D \not\isin M$:}
333 $D \isin C$. Also $D \isin L \lor D \isin R$ so $D \le L \lor D \le
336 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
342 \section{Commit annotation}
344 We annotate each Topbloke commit $C$ with:
348 \baseof{C}, \text{ if } C \in \py
351 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
353 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
356 $\patchof{C}$, for each kind of Topbloke-generated commit, is stated
357 in the summary in the section for that kind of commit.
359 Whether $\baseof{C}$ is required, and if so what the value is, is
360 stated in the proof of Unique Base for each kind of commit.
362 $C \haspatch \pa{Q}$ or $\nothaspatch \pa{Q}$ is represented as the
363 set $\{ \pa{Q} | C \haspatch \pa{Q} \}$. Whether $C \haspatch \pa{Q}$
365 (in terms of $I \haspatch \pa{Q}$ or $I \nothaspatch \pa{Q}$
366 for the ingredients $I$),
367 in the proof of Coherence for each kind of commit.
369 $\pendsof{C}{\pa{Q}^+}$ is computed, for all Topbloke-generated commits,
370 using the lemma Calculation of Ends, above.
371 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
372 make it wrong to make plain commits with git because the recorded $\pends$
373 would have to be updated. The annotation is not needed in that case
374 because $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
376 \section{Simple commit}
378 A simple single-parent forward commit $C$ as made by git-commit.
380 \tag*{} C \hasparents \{ A \} \\
381 \tag*{} \patchof{C} = \patchof{A} \\
382 \tag*{} D \isin C \equiv D \isin A \lor D = C
384 This also covers Topbloke-generated commits on plain git branches:
385 Topbloke strips the metadata when exporting.
387 \subsection{No Replay}
390 \subsection{Unique Base}
391 If $A, C \in \py$ then by Calculation of Ends for
392 $C, \py, C \not\in \py$:
393 $\pendsof{C}{\pn} = \pendsof{A}{\pn}$ so
394 $\baseof{C} = \baseof{A}$. $\qed$
396 \subsection{Tip Contents}
397 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
398 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
399 Substitute into the contents of $C$:
400 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
402 Since $D = C \implies D \in \py$,
403 and substituting in $\baseof{C}$, this gives:
404 \[ D \isin C \equiv D \isin \baseof{C} \lor
405 (D \in \py \land D \le A) \lor
406 (D = C \land D \in \py) \]
407 \[ \equiv D \isin \baseof{C} \lor
408 [ D \in \py \land ( D \le A \lor D = C ) ] \]
409 So by Exact Ancestors:
410 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
414 \subsection{Base Acyclic}
416 Need to consider only $A, C \in \pn$.
418 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
420 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
421 $A$, $D \isin C \implies D \not\in \py$.
425 \subsection{Coherence and patch inclusion}
427 Need to consider $D \in \py$
429 \subsubsection{For $A \haspatch P, D = C$:}
435 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
437 \subsubsection{For $A \haspatch P, D \neq C$:}
438 Ancestors: $ D \le C \equiv D \le A $.
440 Contents: $ D \isin C \equiv D \isin A \lor f $
441 so $ D \isin C \equiv D \isin A $.
444 \[ A \haspatch P \implies C \haspatch P \]
446 \subsubsection{For $A \nothaspatch P$:}
448 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
451 Now by contents of $A$, $D \notin A$, so $D \notin C$.
454 \[ A \nothaspatch P \implies C \nothaspatch P \]
457 \subsection{Foreign inclusion:}
459 If $D = C$, trivial. For $D \neq C$:
460 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
462 \section{Create Base}
464 Given $L$, create a Topbloke base branch initial commit $B$.
466 B \hasparents \{ L \}
470 D \isin B \equiv D \isin L \lor D = B
473 \subsection{Conditions}
475 \[ \eqn{ Ingredients }{
476 \patchof{L} = \pa{L} \lor \patchof{L} = \bot
478 \[ \eqn{ Non-recursion }{
482 \subsection{No Replay}
484 If $\patchof{L} = \pa{L}$, trivial by Base Acyclic for $L$.
486 If $\patchof{L} = \bot$, xxx
488 Trivial from Base Acyclic for $L$. $\qed$
490 \subsection{Unique Base}
492 Not applicable. $\qed$
494 \subsection{Tip Contents}
496 Not applicable. $\qed$
498 \subsection{Base Acyclic}
510 Given $L$ and $\pr$ as represented by $R^+, R^-$.
511 Construct $C$ which has $\pr$ removed.
512 Used for removing a branch dependency.
514 C \hasparents \{ L \}
516 \patchof{C} = \patchof{L}
518 \mergeof{C}{L}{R^+}{R^-}
521 \subsection{Conditions}
523 \[ \eqn{ Ingredients }{
524 R^+ \in \pry \land R^- = \baseof{R^+}
526 \[ \eqn{ Into Base }{
529 \[ \eqn{ Unique Tip }{
530 \pendsof{L}{\pry} = \{ R^+ \}
532 \[ \eqn{ Currently Included }{
536 \subsection{Ordering of ${L, R^+, R^-}$:}
538 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
539 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
542 (Note that $R^+ \not\le R^-$, i.e. the merge base
543 is a descendant, not an ancestor, of the 2nd parent.)
545 \subsection{No Replay}
547 No Replay for Merge Results applies. $\qed$
549 \subsection{Desired Contents}
551 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
554 \subsubsection{For $D = C$:}
556 Trivially $D \isin C$. OK.
558 \subsubsection{For $D \neq C, D \not\le L$:}
560 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
561 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
563 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
565 By Currently Included, $D \isin L$.
567 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
568 by Unique Tip, $D \le R^+ \equiv D \le L$.
571 By Base Acyclic, $D \not\isin R^-$.
573 Apply $\merge$: $D \not\isin C$. OK.
575 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
577 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
579 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
583 \subsection{Unique Base}
585 Into Base means that $C \in \pn$, so Unique Base is not
588 \subsection{Tip Contents}
590 Again, not applicable. $\qed$
592 \subsection{Base Acyclic}
594 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
595 And by Into Base $C \not\in \py$.
596 Now from Desired Contents, above, $D \isin C
597 \implies D \isin L \lor D = C$, which thus
598 $\implies D \not\in \py$. $\qed$.
600 \subsection{Coherence and Patch Inclusion}
602 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
604 \subsubsection{For $\p = \pr$:}
605 By Desired Contents, above, $D \not\isin C$.
606 So $C \nothaspatch \pr$.
608 \subsubsection{For $\p \neq \pr$:}
609 By Desired Contents, $D \isin C \equiv D \isin L$
610 (since $D \in \py$ so $D \not\in \pry$).
612 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
613 So $L \nothaspatch \p \implies C \nothaspatch \p$.
615 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
616 so $L \haspatch \p \implies C \haspatch \p$.
620 \subsection{Foreign Inclusion}
622 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
623 So by Desired Contents $D \isin C \equiv D \isin L$.
624 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
626 And $D \le C \equiv D \le L$.
627 Thus $D \isin C \equiv D \le C$.
633 Merge commits $L$ and $R$ using merge base $M$:
635 C \hasparents \{ L, R \}
637 \patchof{C} = \patchof{L}
641 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
643 \subsection{Conditions}
644 \[ \eqn{ Ingredients }{
647 \[ \eqn{ Tip Merge }{
650 R \in \py : & \baseof{R} \ge \baseof{L}
651 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
652 R \in \pn : & M = \baseof{L} \\
653 \text{otherwise} : & \false
656 \[ \eqn{ Merge Acyclic }{
661 \[ \eqn{ Removal Merge Ends }{
662 X \not\haspatch \p \land
666 \pendsof{Y}{\py} = \pendsof{M}{\py}
668 \[ \eqn{ Addition Merge Ends }{
669 X \not\haspatch \p \land
673 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
677 \subsection{Non-Topbloke merges}
679 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$.
680 I.e. not only is it forbidden to merge into a Topbloke-controlled
681 branch without Topbloke's assistance, it is also forbidden to
682 merge any Topbloke-controlled branch into any plain git branch.
684 Given those conditions, Tip Merge and Merge Acyclic do not apply.
685 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
686 Merge Ends condition applies. Good.
688 \subsection{No Replay}
690 No Replay for Merge Results applies. $\qed$
692 \subsection{Unique Base}
694 Need to consider only $C \in \py$, ie $L \in \py$,
695 and calculate $\pendsof{C}{\pn}$. So we will consider some
696 putative ancestor $A \in \pn$ and see whether $A \le C$.
698 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
699 But $C \in py$ and $A \in \pn$ so $A \neq C$.
700 Thus $A \le C \equiv A \le L \lor A \le R$.
702 By Unique Base of L and Transitive Ancestors,
703 $A \le L \equiv A \le \baseof{L}$.
705 \subsubsection{For $R \in \py$:}
707 By Unique Base of $R$ and Transitive Ancestors,
708 $A \le R \equiv A \le \baseof{R}$.
710 But by Tip Merge condition on $\baseof{R}$,
711 $A \le \baseof{L} \implies A \le \baseof{R}$, so
712 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
713 Thus $A \le C \equiv A \le \baseof{R}$.
714 That is, $\baseof{C} = \baseof{R}$.
716 \subsubsection{For $R \in \pn$:}
718 By Tip Merge condition on $R$ and since $M \le R$,
719 $A \le \baseof{L} \implies A \le R$, so
720 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
721 Thus $A \le C \equiv A \le R$.
722 That is, $\baseof{C} = R$.
726 \subsection{Coherence and Patch Inclusion}
728 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
729 This involves considering $D \in \py$.
731 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
732 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
733 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
734 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
736 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
737 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
738 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
740 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
742 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
743 \equiv D \isin L \lor D \isin R$.
744 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
746 Consider $D \neq C, D \isin X \land D \isin Y$:
747 By $\merge$, $D \isin C$. Also $D \le X$
748 so $D \le C$. OK for $C \haspatch \p$.
750 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
751 By $\merge$, $D \not\isin C$.
752 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
753 OK for $C \haspatch \p$.
755 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
756 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
757 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
758 OK for $C \haspatch \p$.
760 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
762 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
764 $M \haspatch \p \implies C \nothaspatch \p$.
765 $M \nothaspatch \p \implies C \haspatch \p$.
769 One of the Merge Ends conditions applies.
770 Recall that we are considering $D \in \py$.
771 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
772 We will show for each of
773 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
774 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
776 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
777 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
778 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
779 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
781 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
782 $D \le Y$ so $D \le C$.
783 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
785 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
786 $D \not\le Y$. If $D \le X$ then
787 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
788 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
789 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
791 Consider $D \neq C, M \haspatch P, D \isin Y$:
792 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
793 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
794 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
796 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
797 By $\merge$, $D \not\isin C$. OK.
801 \subsection{Base Acyclic}
803 This applies when $C \in \pn$.
804 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
806 Consider some $D \in \py$.
808 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
809 R$. And $D \neq C$. So $D \not\isin C$.
813 \subsection{Tip Contents}
815 We need worry only about $C \in \py$.
816 And $\patchof{C} = \patchof{L}$
817 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
818 of $C$, and its Coherence and Patch Inclusion, as just proved.
820 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
821 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
822 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
823 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
824 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
826 We will consider an arbitrary commit $D$
827 and prove the Exclusive Tip Contents form.
829 \subsubsection{For $D \in \py$:}
830 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
833 \subsubsection{For $D \not\in \py, R \not\in \py$:}
835 $D \neq C$. By Tip Contents of $L$,
836 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
837 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
838 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
839 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
841 \subsubsection{For $D \not\in \py, R \in \py$:}
846 $D \isin L \equiv D \isin \baseof{L}$ and
847 $D \isin R \equiv D \isin \baseof{R}$.
849 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
850 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
851 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
852 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
854 So $D \isin M \equiv D \isin L$ and by $\merge$,
855 $D \isin C \equiv D \isin R$. But from Unique Base,
856 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
860 \subsection{Foreign Inclusion}
862 Consider some $D$ s.t. $\patchof{D} = \bot$.
863 By Foreign Inclusion of $L, M, R$:
864 $D \isin L \equiv D \le L$;
865 $D \isin M \equiv D \le M$;
866 $D \isin R \equiv D \le R$.
868 \subsubsection{For $D = C$:}
870 $D \isin C$ and $D \le C$. OK.
872 \subsubsection{For $D \neq C, D \isin M$:}
874 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
875 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
877 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
879 By $\merge$, $D \isin C$.
880 And $D \isin X$ means $D \le X$ so $D \le C$.
883 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
885 By $\merge$, $D \not\isin C$.
886 And $D \not\le L, D \not\le R$ so $D \not\le C$.