| | Some definitions of interest. |
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| assert | Def  b == if b True else False fi |
| | | Thm*  b: . b  Prop |
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| mapoutl | Def mapoutl(s) == mapfilter( x.outl(x);x.isl(x);s) |
| | | Thm* A,B:Type, s:(A+B) List. mapoutl(s) A List |
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| isl | Def isl(x) == InjCase(x; y. true ; z. false) |
| | | Thm* A,B:Type, x:A+B. isl(x) |
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| l_member | Def (x l) ==  i: . i < ||l|| & x = l[i] T |
| | | Thm* T:Type, x:T, l:T List. (x l) Prop |
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| no_repeats | Def no_repeats(T;l) == i,j:. i < ||l||   j < ||l||  i = j l[i] = l[j] T |
| | | Thm* T:Type, l:T List. no_repeats(T;l) Prop |
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| outl | Def outl(x) == InjCase(x; y. y; z. "???") |
| | | Thm* A,B:Type, x:A+B. isl(x) outl(x) A |
