coloring.pl

color(red).
color(green).
color(blue).
color(yellow).

neighbor(StateAColor, StateBColor) :- 
	color(StateAColor), 
    color(StateBColor), 
    StateAColor \= StateBColor. /* \= is the not equal operator */

germany(BW, BY) :- neighbor(BW, BY).
germany(BW, BY, SL, RP, HE) :- neighbor(BW, BY), neighbor(BW, RP), neighbor(BW, HE).
germany(SH, MV, HH, HB, NI, ST, BE, BB, SN, NW, HE, TH, RP, SL, BW, BY) :- 
neighbor(SH, NI), neighbor(SH, HH), neighbor(SH, MV),
neighbor(HH, NI),
neighbor(MV, NI), neighbor(MV, BB),
neighbor(NI, HB), neighbor(NI, BB), neighbor(NI, ST), neighbor(NI, TH),
neighbor(NI, HE), neighbor(NI, NW),
neighbor(ST, BB), neighbor(ST, SN), neighbor(ST, TH),
neighbor(BB, BE), neighbor(BB, SN),
neighbor(NW, HE), neighbor(NW, RP),
neighbor(SN, TH), neighbor(SN, BY),
neighbor(RP, SL), neighbor(RP, HE), neighbor(RP, BW),
neighbor(HE, BW), neighbor(HE, TH), neighbor(HE, BY),
neighbor(TH, BY),
neighbor(BW, BY).