et c comme ca :
a/a+b+c<a/a+b
b/a+b+d<b/a+b
c/c+d+a<c/c+d
d/c+d+b<d/c+d
doonc :
a/a+b+c + b/a+b+d + c/c+d+a + d/c+d+b<a/a+b + b/a+b + c/c+d +d/c+d
a/a+b+c + b/a+b+d + c/c+d+a + d/c+d+b<a+b/a+b + c+d/c+d
a/a+b+c + b/a+b+d + c/c+d+a + d/c+d+b < 1+1
a/a+b+c + b/a+b+d + c/c+d+a + d/c+d+b < 2