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
310 Consider some $D \le C$. If $D = C$, $\patchof{D} = \bot$ trivially.
311 If $D \neq C$ then $D \le A$ where $A \in \set A$. By Foreign
312 Contents of $A$, $\patchof{D} = \bot$.
315 \subsection{No Replay for Merge Results}
317 If we are constructing $C$, with,
325 No Replay is preserved. \proofstarts
327 \subsubsection{For $D=C$:} $D \isin C, D \le C$. OK.
329 \subsubsection{For $D \isin L \land D \isin R$:}
330 $D \isin C$. And $D \isin L \implies D \le L \implies D \le C$. OK.
332 \subsubsection{For $D \neq C \land D \not\isin L \land D \not\isin R$:}
335 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
336 \land D \not\isin M$:}
337 $D \isin C$. Also $D \isin L \lor D \isin R$ so $D \le L \lor D \le
340 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
346 \section{Commit annotation}
348 We annotate each Topbloke commit $C$ with:
352 \baseof{C}, \text{ if } C \in \py
355 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
357 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
360 $\patchof{C}$, for each kind of Topbloke-generated commit, is stated
361 in the summary in the section for that kind of commit.
363 Whether $\baseof{C}$ is required, and if so what the value is, is
364 stated in the proof of Unique Base for each kind of commit.
366 $C \haspatch \pa{Q}$ or $\nothaspatch \pa{Q}$ is represented as the
367 set $\{ \pa{Q} | C \haspatch \pa{Q} \}$. Whether $C \haspatch \pa{Q}$
369 (in terms of $I \haspatch \pa{Q}$ or $I \nothaspatch \pa{Q}$
370 for the ingredients $I$),
371 in the proof of Coherence for each kind of commit.
373 $\pendsof{C}{\pa{Q}^+}$ is computed, for all Topbloke-generated commits,
374 using the lemma Calculation of Ends, above.
375 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
376 make it wrong to make plain commits with git because the recorded $\pends$
377 would have to be updated. The annotation is not needed in that case
378 because $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
380 \section{Simple commit}
382 A simple single-parent forward commit $C$ as made by git-commit.
384 \tag*{} C \hasparents \{ A \} \\
385 \tag*{} \patchof{C} = \patchof{A} \\
386 \tag*{} D \isin C \equiv D \isin A \lor D = C
388 This also covers Topbloke-generated commits on plain git branches:
389 Topbloke strips the metadata when exporting.
391 \subsection{No Replay}
394 \subsection{Unique Base}
395 If $A, C \in \py$ then by Calculation of Ends for
396 $C, \py, C \not\in \py$:
397 $\pendsof{C}{\pn} = \pendsof{A}{\pn}$ so
398 $\baseof{C} = \baseof{A}$. $\qed$
400 \subsection{Tip Contents}
401 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
402 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
403 Substitute into the contents of $C$:
404 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
406 Since $D = C \implies D \in \py$,
407 and substituting in $\baseof{C}$, this gives:
408 \[ D \isin C \equiv D \isin \baseof{C} \lor
409 (D \in \py \land D \le A) \lor
410 (D = C \land D \in \py) \]
411 \[ \equiv D \isin \baseof{C} \lor
412 [ D \in \py \land ( D \le A \lor D = C ) ] \]
413 So by Exact Ancestors:
414 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
418 \subsection{Base Acyclic}
420 Need to consider only $A, C \in \pn$.
422 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
424 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
425 $A$, $D \isin C \implies D \not\in \py$.
429 \subsection{Coherence and patch inclusion}
431 Need to consider $D \in \py$
433 \subsubsection{For $A \haspatch P, D = C$:}
439 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
441 \subsubsection{For $A \haspatch P, D \neq C$:}
442 Ancestors: $ D \le C \equiv D \le A $.
444 Contents: $ D \isin C \equiv D \isin A \lor f $
445 so $ D \isin C \equiv D \isin A $.
448 \[ A \haspatch P \implies C \haspatch P \]
450 \subsubsection{For $A \nothaspatch P$:}
452 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
455 Now by contents of $A$, $D \notin A$, so $D \notin C$.
458 \[ A \nothaspatch P \implies C \nothaspatch P \]
461 \subsection{Foreign inclusion:}
463 If $D = C$, trivial. For $D \neq C$:
464 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
466 \subsection{Foreign Contents:}
468 Only relevant if $\patchof{C} = \bot$, and in that case Totally
469 Foreign Contents applies. $\qed$
471 \section{Create Base}
473 Given $L$, create a Topbloke base branch initial commit $B$.
475 B \hasparents \{ L \}
477 \patchof{B} = \pan{B}
479 D \isin B \equiv D \isin L \lor D = B
482 \subsection{Conditions}
484 \[ \eqn{ Ingredients }{
485 \patchof{L} = \pa{L} \lor \patchof{L} = \bot
487 \[ \eqn{ Non-recursion }{
491 \subsection{No Replay}
493 If $\patchof{L} = \pa{L}$, trivial by Base Acyclic for $L$.
495 If $\patchof{L} = \bot$, consider some $D \isin B$. $D \neq B$.
496 Thus $D \isin L$. So by No Replay of $D$ in $L$, $D \le L$.
499 \subsection{Unique Base}
503 \subsection{Tip Contents}
507 \subsection{Base Acyclic}
509 Consider some $D \isin B$. If $D = B$, $D \in \pn$, OK.
511 If $D \neq B$, $D \isin L$. By No Replay of $D$ in $L$, $D \le L$.
512 Thus by Foreign Contents of $L$, $\patchof{D} = \bot$. OK.
516 \subsection{Coherence and Patch Inclusion}
518 Consider some $D \in \p$.
519 $B \not\in \py$ so $D \neq B$. So $D \isin B \equiv D \isin L$.
521 Thus $L \haspatch \p \implies B \haspatch P$
522 and $L \nothaspatch \p \implies B \nothaspatch P$.
526 \subsection{Foreign Inclusion}
528 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq B$
529 so $D \isin B \equiv D \isin L$.
530 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
531 And by Exact Ancestors $D \le L \equiv D \le B$.
532 So $D \isin B \equiv D \le B$. $\qed$
540 Given $L$ and $\pr$ as represented by $R^+, R^-$.
541 Construct $C$ which has $\pr$ removed.
542 Used for removing a branch dependency.
544 C \hasparents \{ L \}
546 \patchof{C} = \patchof{L}
548 \mergeof{C}{L}{R^+}{R^-}
551 \subsection{Conditions}
553 \[ \eqn{ Ingredients }{
554 R^+ \in \pry \land R^- = \baseof{R^+}
556 \[ \eqn{ Into Base }{
559 \[ \eqn{ Unique Tip }{
560 \pendsof{L}{\pry} = \{ R^+ \}
562 \[ \eqn{ Currently Included }{
566 \subsection{Ordering of ${L, R^+, R^-}$:}
568 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
569 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$.
572 (Note that $R^+ \not\le R^-$, i.e. the merge base
573 is a descendant, not an ancestor, of the 2nd parent.)
575 \subsection{No Replay}
577 No Replay for Merge Results applies. $\qed$
579 \subsection{Desired Contents}
581 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
584 \subsubsection{For $D = C$:}
586 Trivially $D \isin C$. OK.
588 \subsubsection{For $D \neq C, D \not\le L$:}
590 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
591 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
593 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
595 By Currently Included, $D \isin L$.
597 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
598 by Unique Tip, $D \le R^+ \equiv D \le L$.
601 By Base Acyclic, $D \not\isin R^-$.
603 Apply $\merge$: $D \not\isin C$. OK.
605 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
607 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
609 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
613 \subsection{Unique Base}
615 Into Base means that $C \in \pn$, so Unique Base is not
618 \subsection{Tip Contents}
620 Again, not applicable. $\qed$
622 \subsection{Base Acyclic}
624 By Base Acyclic for $L$, $D \isin L \implies D \not\in \py$.
625 And by Into Base $C \not\in \py$.
626 Now from Desired Contents, above, $D \isin C
627 \implies D \isin L \lor D = C$, which thus
628 $\implies D \not\in \py$. $\qed$.
630 \subsection{Coherence and Patch Inclusion}
632 Need to consider some $D \in \py$. By Into Base, $D \neq C$.
634 \subsubsection{For $\p = \pr$:}
635 By Desired Contents, above, $D \not\isin C$.
636 So $C \nothaspatch \pr$.
638 \subsubsection{For $\p \neq \pr$:}
639 By Desired Contents, $D \isin C \equiv D \isin L$
640 (since $D \in \py$ so $D \not\in \pry$).
642 If $L \nothaspatch \p$, $D \not\isin L$ so $D \not\isin C$.
643 So $L \nothaspatch \p \implies C \nothaspatch \p$.
645 Whereas if $L \haspatch \p$, $D \isin L \equiv D \le L$.
646 so $L \haspatch \p \implies C \haspatch \p$.
650 \subsection{Foreign Inclusion}
652 Consider some $D$ s.t. $\patchof{D} = \bot$. $D \neq C$.
653 So by Desired Contents $D \isin C \equiv D \isin L$.
654 By Foreign Inclusion of $D$ in $L$, $D \isin L \equiv D \le L$.
656 And $D \le C \equiv D \le L$.
657 Thus $D \isin C \equiv D \le C$.
661 \subsection{Foreign Contents}
667 Merge commits $L$ and $R$ using merge base $M$:
669 C \hasparents \{ L, R \}
671 \patchof{C} = \patchof{L}
675 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
677 \subsection{Conditions}
678 \[ \eqn{ Ingredients }{
681 \[ \eqn{ Tip Merge }{
684 R \in \py : & \baseof{R} \ge \baseof{L}
685 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
686 R \in \pn : & M = \baseof{L} \\
687 \text{otherwise} : & \false
690 \[ \eqn{ Merge Acyclic }{
695 \[ \eqn{ Removal Merge Ends }{
696 X \not\haspatch \p \land
700 \pendsof{Y}{\py} = \pendsof{M}{\py}
702 \[ \eqn{ Addition Merge Ends }{
703 X \not\haspatch \p \land
707 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
710 \[ \eqn{ Foreign Merges }{
711 \patchof{L} = \bot \equiv \patchof{R} = \bot
714 \subsection{Non-Topbloke merges}
716 We require both $\patchof{L} = \bot$ and $\patchof{R} = \bot$
717 (Foreign Merges, above).
718 I.e. not only is it forbidden to merge into a Topbloke-controlled
719 branch without Topbloke's assistance, it is also forbidden to
720 merge any Topbloke-controlled branch into any plain git branch.
722 Given those conditions, Tip Merge and Merge Acyclic do not apply.
723 And $Y \not\in \py$ so $\neg [ Y \haspatch \p ]$ so neither
724 Merge Ends condition applies.
726 So a plain git merge of non-Topbloke branches meets the conditions and
727 is therefore consistent with our scheme.
729 \subsection{No Replay}
731 No Replay for Merge Results applies. $\qed$
733 \subsection{Unique Base}
735 Need to consider only $C \in \py$, ie $L \in \py$,
736 and calculate $\pendsof{C}{\pn}$. So we will consider some
737 putative ancestor $A \in \pn$ and see whether $A \le C$.
739 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
740 But $C \in py$ and $A \in \pn$ so $A \neq C$.
741 Thus $A \le C \equiv A \le L \lor A \le R$.
743 By Unique Base of L and Transitive Ancestors,
744 $A \le L \equiv A \le \baseof{L}$.
746 \subsubsection{For $R \in \py$:}
748 By Unique Base of $R$ and Transitive Ancestors,
749 $A \le R \equiv A \le \baseof{R}$.
751 But by Tip Merge condition on $\baseof{R}$,
752 $A \le \baseof{L} \implies A \le \baseof{R}$, so
753 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
754 Thus $A \le C \equiv A \le \baseof{R}$.
755 That is, $\baseof{C} = \baseof{R}$.
757 \subsubsection{For $R \in \pn$:}
759 By Tip Merge condition on $R$ and since $M \le R$,
760 $A \le \baseof{L} \implies A \le R$, so
761 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
762 Thus $A \le C \equiv A \le R$.
763 That is, $\baseof{C} = R$.
767 \subsection{Coherence and Patch Inclusion}
769 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
770 This involves considering $D \in \py$.
772 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
773 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
774 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
775 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
777 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
778 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
779 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
781 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
783 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
784 \equiv D \isin L \lor D \isin R$.
785 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
787 Consider $D \neq C, D \isin X \land D \isin Y$:
788 By $\merge$, $D \isin C$. Also $D \le X$
789 so $D \le C$. OK for $C \haspatch \p$.
791 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
792 By $\merge$, $D \not\isin C$.
793 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
794 OK for $C \haspatch \p$.
796 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
797 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
798 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
799 OK for $C \haspatch \p$.
801 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
803 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
805 $M \haspatch \p \implies C \nothaspatch \p$.
806 $M \nothaspatch \p \implies C \haspatch \p$.
810 One of the Merge Ends conditions applies.
811 Recall that we are considering $D \in \py$.
812 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
813 We will show for each of
814 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
815 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
817 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
818 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
819 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
820 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
822 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
823 $D \le Y$ so $D \le C$.
824 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
826 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
827 $D \not\le Y$. If $D \le X$ then
828 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
829 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
830 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
832 Consider $D \neq C, M \haspatch P, D \isin Y$:
833 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
834 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
835 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
837 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
838 By $\merge$, $D \not\isin C$. OK.
842 \subsection{Base Acyclic}
844 This applies when $C \in \pn$.
845 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
847 Consider some $D \in \py$.
849 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
850 R$. And $D \neq C$. So $D \not\isin C$.
854 \subsection{Tip Contents}
856 We need worry only about $C \in \py$.
857 And $\patchof{C} = \patchof{L}$
858 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
859 of $C$, and its Coherence and Patch Inclusion, as just proved.
861 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
862 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
863 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
864 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
865 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
867 We will consider an arbitrary commit $D$
868 and prove the Exclusive Tip Contents form.
870 \subsubsection{For $D \in \py$:}
871 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
874 \subsubsection{For $D \not\in \py, R \not\in \py$:}
876 $D \neq C$. By Tip Contents of $L$,
877 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
878 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
879 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
880 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
882 \subsubsection{For $D \not\in \py, R \in \py$:}
887 $D \isin L \equiv D \isin \baseof{L}$ and
888 $D \isin R \equiv D \isin \baseof{R}$.
890 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
891 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
892 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
893 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
895 So $D \isin M \equiv D \isin L$ and by $\merge$,
896 $D \isin C \equiv D \isin R$. But from Unique Base,
897 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
901 \subsection{Foreign Inclusion}
903 Consider some $D$ s.t. $\patchof{D} = \bot$.
904 By Foreign Inclusion of $L, M, R$:
905 $D \isin L \equiv D \le L$;
906 $D \isin M \equiv D \le M$;
907 $D \isin R \equiv D \le R$.
909 \subsubsection{For $D = C$:}
911 $D \isin C$ and $D \le C$. OK.
913 \subsubsection{For $D \neq C, D \isin M$:}
915 Thus $D \le M$ so $D \le L$ and $D \le R$ so $D \isin L$ and $D \isin
916 R$. So by $\merge$, $D \isin C$. And $D \le C$. OK.
918 \subsubsection{For $D \neq C, D \not\isin M, D \isin X$:}
920 By $\merge$, $D \isin C$.
921 And $D \isin X$ means $D \le X$ so $D \le C$.
924 \subsubsection{For $D \neq C, D \not\isin M, D \not\isin L, D \not\isin R$:}
926 By $\merge$, $D \not\isin C$.
927 And $D \not\le L, D \not\le R$ so $D \not\le C$.
932 \subsection{Foreign Contents}
934 Only relevant if $\patchof{L} = \bot$, in which case
935 $\patchof{C} = \bot$ and by Foreign Merges $\patchof{R} = \bot$,
936 so Totally Foreign Contents applies. $\qed$