Rem $x+y=[x_{\min}+y_{\min},x_{\max}+y_{\max}]$ Function int_add(x, y) Dim res(2) As Double res(0) = x(1) + y(1): res(1) = x(2) + y(2) int_add = res End Function Rem $x-y=[x_{\min}-y_{\max},x_{\max}-y_{\min}]$ Function int_subt(x, y) Dim res(2) As Double res(0) = x(1) - y(2): res(1) = x(2) - y(1) int_subt = res End Function Function min(x, y) If x < y Then min = x Else min = y End Function Function max(x, y) If x > y Then max = x Else max = y End Function Rem $x\cdot y=\bigl[\min(x_{\min}y_{\min},x_{\min}y_{\max},x_{\max}y_{\min},x_{\max}y_{\max}),$ Rem \hskip 14mm $\max(x_{\min}y_{\min},x_{\min}y_{\max},x_{\max}y_{\min},x_{\max}y_{\max})\bigr]$ Function int_mul(x, y) Dim tmp(4) As Double Dim res(2) As Double tmp(0) = x(1) * y(1): tmp(1) = x(1) * y(2) tmp(2) = x(2) * y(1): tmp(3) = x(2) * y(2) res(0) = min(min(tmp(0), tmp(1)), min(tmp(2), tmp(3))) res(1) = max(max(tmp(0), tmp(1)), max(tmp(2), tmp(3))) int_mul = res End Function Rem $x/y=x\cdot[1/y_{\max},1/y_{\min}]$ Function int_div(x, y) Dim tmp(2) As Double tmp(1) = 1 / y(2): tmp(2) = 1 / y(1) int_div = int_mul(x, tmp) End Function Rem $\mathbb R\to\mathbb{IR}$ Function interval(x As Double) Dim res(2) As Double res(0) = x: res(1) = x interval = res End Function