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fun quadrat(x)                   = x * x;
fun summe_quadrate(x,y)          = quadrat(x) + quadrat(y); 
fun pythagorasrelation(a,b,c)    = (summe_quadrate(a,b) = quadrat(c));
fun pythagoraszahl(z)            = pythagorasrelation(z-1, z, z+1);
val ist_4_pythagoraszahl         = pythagoraszahl(4);