| biject | Def Bij(A; B; f) == Inj(A; B; f)  &  Surj(A; B; f) Thm*  | 
| int_seg | Def {i..j  } == {k:  | i  k  <  j } Thm*  | 
| inv_funs | Def InvFuns(A; B; f; g) == g o f = Id  &  f o g = Id Thm*  | 
| nat | Def  == {i:  | 0  i } 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*  | 
| lelt | Def i  j  <  k == i  j  &  j < k | 
| tidentity | Def Id == Id Thm*  | 
| compose | Def (f o g)(x) == f(g(x)) Thm*  | 
| le | Def A  B ==  B < A Thm*  | 
| identity | Def Id(x) == x Thm*  | 
| not | Def  A == A   False Thm*  | 
About:
|  |  |  |  |  |  |  |  | 
|  |  |  |  |  |  |  |  |