\     Here the variable x12c2  is 1 or 0 according to
\     whether or not the row 1, col 2 square has 
\     colour number 2
\ The objective is unimportant, since we are interested in feasibility
  Maximize
  x11c1
Subject To
\ Values specified by the puzzle
  x21c2 = 1
\ Square 11 has one of the two colours
  x11c1 + x11c2 = 1
\ Similarly for all other squares:
  x12c1 + x12c2 = 1
  x21c1 + x21c2 = 1
  x22c1 + x22c2 = 1
\ Row 1: all colours occur once:
  x11c1 + x12c1 = 1
  x11c2 + x12c2 = 1
\ Same for row 2
  x21c1 + x22c1 = 1
  x21c2 + x22c2 = 1
\ Same for the columns
  x11c1 + x21c1 = 1
  x11c2 + x21c2 = 1
\ 
  x12c1 + x22c1 = 1
  x12c2 + x22c2 = 1
Binary
  x11c1 x11c2 x12c1 x12c2 x21c1 x21c2 x22c1 x22c2 
End