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
174 Some (overlapping) alternative formulations:
176 $\displaystyle D \isin C \equiv
178 D \isin L \equiv D \isin R : & D = C \lor D \isin L \\
179 D \isin L \equiv D \isin R : & D = C \lor D \isin R \\
180 D \isin L \nequiv D \isin R : & D = C \lor D \not\isin M \\
181 D \isin M \equiv D \isin L : & D = C \lor D \isin R \\
182 D \isin M \equiv D \isin R : & D = C \lor D \isin L \\
190 We maintain these each time we construct a new commit. \\
192 C \has D \implies C \ge D
194 \[\eqn{Unique Base:}{
195 \bigforall_{C \in \py} \pendsof{C}{\pn} = \{ B \}
197 \[\eqn{Tip Contents:}{
198 \bigforall_{C \in \py} D \isin C \equiv
199 { D \isin \baseof{C} \lor \atop
200 (D \in \py \land D \le C) }
202 \[\eqn{Base Acyclic:}{
203 \bigforall_{B \in \pn} D \isin B \implies D \notin \py
206 \bigforall_{C,\p} C \haspatch \p \lor C \nothaspatch \p
208 \[\eqn{Foreign Inclusion:}{
209 \bigforall_{D \text{ s.t. } \patchof{D} = \bot} D \isin C \equiv D \leq C
212 \section{Some lemmas}
214 \[ \eqn{Exclusive Tip Contents:}{
215 \bigforall_{C \in \py}
216 \neg \Bigl[ D \isin \baseof{C} \land ( D \in \py \land D \le C )
219 Ie, the two limbs of the RHS of Tip Contents are mutually exclusive.
222 Let $B = \baseof{C}$ in $D \isin \baseof{C}$. Now $B \in \pn$.
223 So by Base Acyclic $D \isin B \implies D \notin \py$.
225 \[ \eqntag{{\it Corollary - equivalent to Tip Contents}}{
226 \bigforall_{C \in \py} D \isin C \equiv
228 D \in \py : & D \le C \\
229 D \not\in \py : & D \isin \baseof{C}
233 \[ \eqn{Tip Self Inpatch:}{
234 \bigforall_{C \in \py} C \haspatch \p
236 Ie, tip commits contain their own patch.
239 Apply Exclusive Tip Contents to some $D \in \py$:
240 $ \bigforall_{C \in \py}\bigforall_{D \in \py}
241 D \isin C \equiv D \le C $
244 \[ \eqn{Exact Ancestors:}{
245 \bigforall_{ C \hasparents \set{R} }
247 ( \mathop{\hbox{\huge{$\vee$}}}_{R \in \set R} D \le R )
251 \[ \eqn{Transitive Ancestors:}{
252 \left[ \bigforall_{ E \in \pendsof{C}{\set P} } E \le M \right] \equiv
253 \left[ \bigforall_{ A \in \pancsof{C}{\set P} } A \le M \right]
257 The implication from right to left is trivial because
258 $ \pends() \subset \pancs() $.
259 For the implication from left to right:
260 by the definition of $\mathcal E$,
261 for every such $A$, either $A \in \pends()$ which implies
262 $A \le M$ by the LHS directly,
263 or $\exists_{A' \in \pancs()} \; A' \neq A \land A \le A' $
264 in which case we repeat for $A'$. Since there are finitely many
265 commits, this terminates with $A'' \in \pends()$, ie $A'' \le M$
266 by the LHS. And $A \le A''$.
268 \[ \eqn{Calculation Of Ends:}{
269 \bigforall_{C \hasparents \set A}
270 \pendsof{C}{\set P} =
272 \Bigl[ \Largeexists_{A \in \set A}
273 E \in \pendsof{A}{\set P} \Bigr] \land
274 \Bigl[ \Largenexists_{B \in \set A}
275 E \neq B \land E \le B \Bigr]
280 \subsection{No Replay for Merge Results}
282 If we are constructing $C$, with,
290 No Replay is preserved. \proofstarts
292 \subsubsection{For $D=C$:} $D \isin C, D \le C$. OK.
294 \subsubsection{For $D \isin L \land D \isin R$:}
295 $D \isin C$. And $D \isin L \implies D \le L \implies D \le C$. OK.
297 \subsubsection{For $D \neq C \land D \not\isin L \land D \not\isin R$:}
300 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
301 \land D \not\isin M$:}
302 $D \isin C$. Also $D \isin L \lor D \isin R$ so $D \le L \lor D \le
305 \subsubsection{For $D \neq C \land (D \isin L \equiv D \not\isin R)
311 \section{Commit annotation}
313 We annotate each Topbloke commit $C$ with:
317 \baseof{C}, \text{ if } C \in \py
320 \text{ either } C \haspatch \pa{Q} \text{ or } C \nothaspatch \pa{Q}
322 \bigforall_{\pay{Q} \not\ni C} \pendsof{C}{\pay{Q}}
325 We do not annotate $\pendsof{C}{\py}$ for $C \in \py$. Doing so would
326 make it wrong to make plain commits with git because the recorded $\pends$
327 would have to be updated. The annotation is not needed because
328 $\forall_{\py \ni C} \; \pendsof{C}{\py} = \{C\}$.
330 \section{Simple commit}
332 A simple single-parent forward commit $C$ as made by git-commit.
334 \tag*{} C \hasparents \{ A \} \\
335 \tag*{} \patchof{C} = \patchof{A} \\
336 \tag*{} D \isin C \equiv D \isin A \lor D = C
339 \subsection{No Replay}
342 \subsection{Unique Base}
343 If $A, C \in \py$ then $\baseof{C} = \baseof{A}$. $\qed$
345 \subsection{Tip Contents}
346 We need to consider only $A, C \in \py$. From Tip Contents for $A$:
347 \[ D \isin A \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A ) \]
348 Substitute into the contents of $C$:
349 \[ D \isin C \equiv D \isin \baseof{A} \lor ( D \in \py \land D \le A )
351 Since $D = C \implies D \in \py$,
352 and substituting in $\baseof{C}$, this gives:
353 \[ D \isin C \equiv D \isin \baseof{C} \lor
354 (D \in \py \land D \le A) \lor
355 (D = C \land D \in \py) \]
356 \[ \equiv D \isin \baseof{C} \lor
357 [ D \in \py \land ( D \le A \lor D = C ) ] \]
358 So by Exact Ancestors:
359 \[ D \isin C \equiv D \isin \baseof{C} \lor ( D \in \py \land D \le C
363 \subsection{Base Acyclic}
365 Need to consider only $A, C \in \pn$.
367 For $D = C$: $D \in \pn$ so $D \not\in \py$. OK.
369 For $D \neq C$: $D \isin C \equiv D \isin A$, so by Base Acyclic for
370 $A$, $D \isin C \implies D \not\in \py$. $\qed$
372 \subsection{Coherence and patch inclusion}
374 Need to consider $D \in \py$
376 \subsubsection{For $A \haspatch P, D = C$:}
382 $ D \isin C \equiv \ldots \lor \true \text{ so } D \haspatch C $.
384 \subsubsection{For $A \haspatch P, D \neq C$:}
385 Ancestors: $ D \le C \equiv D \le A $.
387 Contents: $ D \isin C \equiv D \isin A \lor f $
388 so $ D \isin C \equiv D \isin A $.
391 \[ A \haspatch P \implies C \haspatch P \]
393 \subsubsection{For $A \nothaspatch P$:}
395 Firstly, $C \not\in \py$ since if it were, $A \in \py$.
398 Now by contents of $A$, $D \notin A$, so $D \notin C$.
401 \[ A \nothaspatch P \implies C \nothaspatch P \]
404 \subsection{Foreign inclusion:}
406 If $D = C$, trivial. For $D \neq C$:
407 $D \isin C \equiv D \isin A \equiv D \le A \equiv D \le C$. $\qed$
411 Given $L, R^+, R^-$ where
412 $R^+ \in \pry, R^- = \baseof{R^+}$.
413 Construct $C$ which has $\pr$ removed.
414 Used for removing a branch dependency.
416 C \hasparents \{ L \}
418 \patchof{C} = \patchof{L}
420 \mergeof{C}{L}{R^+}{R^-}
423 \subsection{Conditions}
425 \[ \eqn{ Unique Tip }{
426 \pendsof{L}{\pry} = \{ R^+ \}
428 \[ \eqn{ Currently Included }{
435 \subsection{No Replay}
437 By Unique Tip, $R^+ \le L$. By definition of $\base$, $R^- \le R^+$
438 so $R^- \le L$. So $R^+ \le C$ and $R^- \le C$ and No Replay for
439 Merge Results applies. $\qed$
441 \subsection{Desired Contents}
443 \[ D \isin C \equiv [ D \notin \pry \land D \isin L ] \lor D = C \]
446 \subsubsection{For $D = C$:}
448 Trivially $D \isin C$. OK.
450 \subsubsection{For $D \neq C, D \not\le L$:}
452 By No Replay $D \not\isin L$. Also $D \not\le R^-$ hence
453 $D \not\isin R^-$. Thus $D \not\isin C$. OK.
455 \subsubsection{For $D \neq C, D \le L, D \in \pry$:}
457 By Currently Included, $D \isin L$.
459 By Tip Self Inpatch, $D \isin R^+ \equiv D \le R^+$, but by
460 by Unique Tip, $D \le R^+ \equiv D \le L$.
463 By Base Acyclic, $D \not\isin R^-$.
465 Apply $\merge$: $D \not\isin C$. OK.
467 \subsubsection{For $D \neq C, D \le L, D \notin \pry$:}
469 By Tip Contents for $R^+$, $D \isin R^+ \equiv D \isin R^-$.
471 Apply $\merge$: $D \isin C \equiv D \isin L$. OK.
475 \subsection{Unique Base}
477 Need to consider only $C \in \py$, ie $L \in \py$.
481 xxx need to finish anticommit
485 Merge commits $L$ and $R$ using merge base $M$ ($M < L, M < R$):
487 C \hasparents \{ L, R \}
489 \patchof{C} = \patchof{L}
493 We will occasionally use $X,Y$ s.t. $\{X,Y\} = \{L,R\}$.
495 \subsection{Conditions}
497 \[ \eqn{ Tip Merge }{
500 R \in \py : & \baseof{R} \ge \baseof{L}
501 \land [\baseof{L} = M \lor \baseof{L} = \baseof{M}] \\
502 R \in \pn : & M = \baseof{L} \\
503 \text{otherwise} : & \false
506 \[ \eqn{ Merge Acyclic }{
511 \[ \eqn{ Removal Merge Ends }{
512 X \not\haspatch \p \land
516 \pendsof{Y}{\py} = \pendsof{M}{\py}
518 \[ \eqn{ Addition Merge Ends }{
519 X \not\haspatch \p \land
523 \bigforall_{E \in \pendsof{X}{\py}} E \le Y
527 \subsection{No Replay}
529 See No Replay for Merge Results.
531 \subsection{Unique Base}
533 Need to consider only $C \in \py$, ie $L \in \py$,
534 and calculate $\pendsof{C}{\pn}$. So we will consider some
535 putative ancestor $A \in \pn$ and see whether $A \le C$.
537 By Exact Ancestors for C, $A \le C \equiv A \le L \lor A \le R \lor A = C$.
538 But $C \in py$ and $A \in \pn$ so $A \neq C$.
539 Thus $A \le C \equiv A \le L \lor A \le R$.
541 By Unique Base of L and Transitive Ancestors,
542 $A \le L \equiv A \le \baseof{L}$.
544 \subsubsection{For $R \in \py$:}
546 By Unique Base of $R$ and Transitive Ancestors,
547 $A \le R \equiv A \le \baseof{R}$.
549 But by Tip Merge condition on $\baseof{R}$,
550 $A \le \baseof{L} \implies A \le \baseof{R}$, so
551 $A \le \baseof{R} \lor A \le \baseof{L} \equiv A \le \baseof{R}$.
552 Thus $A \le C \equiv A \le \baseof{R}$.
553 That is, $\baseof{C} = \baseof{R}$.
555 \subsubsection{For $R \in \pn$:}
557 By Tip Merge condition on $R$ and since $M \le R$,
558 $A \le \baseof{L} \implies A \le R$, so
559 $A \le R \lor A \le \baseof{L} \equiv A \le R$.
560 Thus $A \le C \equiv A \le R$.
561 That is, $\baseof{C} = R$.
565 \subsection{Coherence and Patch Inclusion}
567 Need to determine $C \haspatch \p$ based on $L,M,R \haspatch \p$.
568 This involves considering $D \in \py$.
570 \subsubsection{For $L \nothaspatch \p, R \nothaspatch \p$:}
571 $D \not\isin L \land D \not\isin R$. $C \not\in \py$ (otherwise $L
572 \in \py$ ie $L \haspatch \p$ by Tip Self Inpatch). So $D \neq C$.
573 Applying $\merge$ gives $D \not\isin C$ i.e. $C \nothaspatch \p$.
575 \subsubsection{For $L \haspatch \p, R \haspatch \p$:}
576 $D \isin L \equiv D \le L$ and $D \isin R \equiv D \le R$.
577 (Likewise $D \isin X \equiv D \le X$ and $D \isin Y \equiv D \le Y$.)
579 Consider $D = C$: $D \isin C$, $D \le C$, OK for $C \haspatch \p$.
581 For $D \neq C$: $D \le C \equiv D \le L \lor D \le R
582 \equiv D \isin L \lor D \isin R$.
583 (Likewise $D \le C \equiv D \le X \lor D \le Y$.)
585 Consider $D \neq C, D \isin X \land D \isin Y$:
586 By $\merge$, $D \isin C$. Also $D \le X$
587 so $D \le C$. OK for $C \haspatch \p$.
589 Consider $D \neq C, D \not\isin X \land D \not\isin Y$:
590 By $\merge$, $D \not\isin C$.
591 And $D \not\le X \land D \not\le Y$ so $D \not\le C$.
592 OK for $C \haspatch \p$.
594 Remaining case, wlog, is $D \not\isin X \land D \isin Y$.
595 $D \not\le X$ so $D \not\le M$ so $D \not\isin M$.
596 Thus by $\merge$, $D \isin C$. And $D \le Y$ so $D \le C$.
597 OK for $C \haspatch \p$.
599 So indeed $L \haspatch \p \land R \haspatch \p \implies C \haspatch \p$.
601 \subsubsection{For (wlog) $X \not\haspatch \p, Y \haspatch \p$:}
603 $C \haspatch \p \equiv M \nothaspatch \p$.
607 One of the Merge Ends conditions applies.
608 Recall that we are considering $D \in \py$.
609 $D \isin Y \equiv D \le Y$. $D \not\isin X$.
610 We will show for each of
611 various cases that $D \isin C \equiv M \nothaspatch \p \land D \le C$
612 (which suffices by definition of $\haspatch$ and $\nothaspatch$).
614 Consider $D = C$: Thus $C \in \py, L \in \py$, and by Tip
615 Self Inpatch $L \haspatch \p$, so $L=Y, R=X$. By Tip Merge,
616 $M=\baseof{L}$. So by Base Acyclic $D \not\isin M$, i.e.
617 $M \nothaspatch \p$. And indeed $D \isin C$ and $D \le C$. OK.
619 Consider $D \neq C, M \nothaspatch P, D \isin Y$:
620 $D \le Y$ so $D \le C$.
621 $D \not\isin M$ so by $\merge$, $D \isin C$. OK.
623 Consider $D \neq C, M \nothaspatch P, D \not\isin Y$:
624 $D \not\le Y$. If $D \le X$ then
625 $D \in \pancsof{X}{\py}$, so by Addition Merge Ends and
626 Transitive Ancestors $D \le Y$ --- a contradiction, so $D \not\le X$.
627 Thus $D \not\le C$. By $\merge$, $D \not\isin C$. OK.
629 Consider $D \neq C, M \haspatch P, D \isin Y$:
630 $D \le Y$ so $D \in \pancsof{Y}{\py}$ so by Removal Merge Ends
631 and Transitive Ancestors $D \in \pancsof{M}{\py}$ so $D \le M$.
632 Thus $D \isin M$. By $\merge$, $D \not\isin C$. OK.
634 Consider $D \neq C, M \haspatch P, D \not\isin Y$:
635 By $\merge$, $D \not\isin C$. OK.
639 \subsection{Base Acyclic}
641 This applies when $C \in \pn$.
642 $C \in \pn$ when $L \in \pn$ so by Merge Acyclic, $R \nothaspatch \p$.
644 Consider some $D \in \py$.
646 By Base Acyclic of $L$, $D \not\isin L$. By the above, $D \not\isin
647 R$. And $D \neq C$. So $D \not\isin C$. $\qed$
649 \subsection{Tip Contents}
651 We need worry only about $C \in \py$.
652 And $\patchof{C} = \patchof{L}$
653 so $L \in \py$ so $L \haspatch \p$. We will use the Unique Base
654 of $C$, and its Coherence and Patch Inclusion, as just proved.
656 Firstly we show $C \haspatch \p$: If $R \in \py$, then $R \haspatch
657 \p$ and by Coherence/Inclusion $C \haspatch \p$ . If $R \not\in \py$
658 then by Tip Merge $M = \baseof{L}$ so by Base Acyclic and definition
659 of $\nothaspatch$, $M \nothaspatch \p$. So by Coherence/Inclusion $C
660 \haspatch \p$ (whether $R \haspatch \p$ or $\nothaspatch$).
662 We will consider an arbitrary commit $D$
663 and prove the Exclusive Tip Contents form.
665 \subsubsection{For $D \in \py$:}
666 $C \haspatch \p$ so by definition of $\haspatch$, $D \isin C \equiv D
669 \subsubsection{For $D \not\in \py, R \not\in \py$:}
671 $D \neq C$. By Tip Contents of $L$,
672 $D \isin L \equiv D \isin \baseof{L}$, and by Tip Merge condition,
673 $D \isin L \equiv D \isin M$. So by definition of $\merge$, $D \isin
674 C \equiv D \isin R$. And $R = \baseof{C}$ by Unique Base of $C$.
675 Thus $D \isin C \equiv D \isin \baseof{C}$. OK.
677 \subsubsection{For $D \not\in \py, R \in \py$:}
682 $D \isin L \equiv D \isin \baseof{L}$ and
683 $D \isin R \equiv D \isin \baseof{R}$.
685 If $\baseof{L} = M$, trivially $D \isin M \equiv D \isin \baseof{L}.$
686 Whereas if $\baseof{L} = \baseof{M}$, by definition of $\base$,
687 $\patchof{M} = \patchof{L} = \py$, so by Tip Contents of $M$,
688 $D \isin M \equiv D \isin \baseof{M} \equiv D \isin \baseof{L}$.
690 So $D \isin M \equiv D \isin L$ and by $\merge$,
691 $D \isin C \equiv D \isin R$. But from Unique Base,
692 $\baseof{C} = R$ so $D \isin C \equiv D \isin \baseof{C}$. OK.
696 xxx up to here, need to prove other things about merges