| Some definitions of interest. |
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sigma_to_union | Def sigma_to_union(e) == e/i,u. if i= 0 inl(u) else inr(u) fi |
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| Thm* A,B:Type. sigma_to_union (i: 2 if i= 0 A else B fi) (A+B) |
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eq_int | Def i= j == if i=j true ; false fi |
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| Thm* i,j: . (i= j)  |
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int_seg | Def {i..j } == {k: | i k < j } |
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| Thm* m,n: . {m..n } Type |
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inv_funs_2 | Def InvFuns(A;B;f;g) == ( x:A. g(f(x)) = x) & ( y:B. f(g(y)) = y) |
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| Thm* f:(A B), g:(B A). InvFuns(A;B;f;g) Prop |
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union_to_sigma | Def union_to_sigma(e) == InjCase(e; a. <0,a>; b. <1,b>) |
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| Thm* A,B:Type. union_to_sigma (A+B) (i: 2 if i= 0 A else B fi) |