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Some definitions of interest.
fappend Def f[n:=x](i) == if i=n x else f(i) fi
Thm* n,m:, f:(nm), x:m. f[n:=x] (n+1)m
increasing Def increasing(f;k) == i:(k-1). f(i) < f(i+1)
Thm* k:, f:(k). increasing(f;k) Prop
int_seg Def {i..j} == {k:| i k < j }
Thm* m,n:. {m..n} Type
nat_plus Def == {i:| 0 < i }
Thm* Type

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ifthenelseintnatural_numberaddsubtractless_thanset
applyfunctionuniversememberpropall!abstraction

Definitions graph 1 2 Sections Graphs Doc