Thm* 
A,B:Type, f:(A
B). Bij(A; B; f) 
Prop
b:B. 
a:A. f(a) = b
Thm* A,B:Type, f:(AB). Surj(A; B; f) Prop
a1,a2:A. f(a1) = f(a2) B 
a1 = a2
Thm* A,B:Type, f:(AB). Inj(A; B; f) Prop
| biject |
Def Bij(A; B; f) == Inj(A; B; f) & Surj(A; B; f)
Thm* |
| surject |
Def Surj(A; B; f) == b:B. a:A. f(a) = b
Thm* |
| inject |
Def Inj(A; B; f) == a1,a2:A. f(a1) = f(a2) B a1 = a2
Thm* |
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