Reference: INTEGRAL

∫(expr, var, a, b) computes the definite integral of expr (the integrand, a string representing a real-valued expression) with the variable var, a string representing a valid identifier that may occur inside expr, between the values a and b of the independent variable var.

Examples: ∫("sin(x)", "x", 0, π) = 2
          ∫("exp(sin(x))", "x", 0, 5) = 7.18911925363