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);