Mathdle 256b

Author:     Logiker/VCC
Category:   Nano Game Oldschool
System:	    Commodore C64

Description:
Aka: Worlde with numbers.
Diophantine equation with 4 unknowns.
x=a+b*c-d
Guess a,b,c,d ∈ [0,9]
x is given

New implementation as Tic-80 works quite differently.