let n be Nat; ( 73 divides n iff 73 divides (value ((mid ((digits (n,10)),2,(len (digits (n,10))))),10)) + (22 * ((digits (n,10)) . 0)) )
reconsider p = 73 as prime Nat by Th32;
A1:
(10 * 22) - 1 = p * 3
;
p,10 are_coprime
by EULER_1:2;
hence
( 73 divides n iff 73 divides (value ((mid ((digits (n,10)),2,(len (digits (n,10))))),10)) + (22 * ((digits (n,10)) . 0)) )
by Th38, A1; verum