Interacting with CLP($\Re$) (I)

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CLP($\Re$) can solve linear (dis)equations:

?- 4 - Y = 3.
Y = 1

?- X = 3*Y - X/2, X+Y = Y - 4*X + 7.
Y = 0.7, X = 1.4

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Sometimes giving a uniquely defined solution is not possible:

?- X+Y <= 7, X-Y >= 8, X+3*Y = -8*Y-2*X.
X = -3.66667*Y, Y <= -1.71429, -2.625 <= Y

(i.e., $-2.625 \leq Y \leq -1.71429, Y = - \frac{X}{3.66667}$)