# boy meets girl
# Robin Snyder, after Martin Gardner


# There are 3 boys and 3 girls.
# One girl is dressed in red, one in green, one in blue. 
# One boy is dressed in red, one in green, one in blue. 

boy	red green blue
girl	red green blue


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# The boy in red danced with the girl in green.

boy,girl	a(red, green).

# No boy danced with a girl who was dressed in the same color.

boy,girl	c(red, X) :- X \= red.
boy,girl	d(green, X) :- X \= green.
boy,girl	e(blue, X) :- X \= blue.