    1:- module(interval, [interval/2, interval/3, op(150, xfx, ...)]).

Perform arithmetic operations with intervals.

An interval is represented as L...U, where L stands for the lower bound and U for the upper bound. If the upper bound is a negative number, it has to be written with an additional space, e.g., -3... -2, or in the infix notation, ...(-3, -2). The choice of using consult and not the module system is motivated by need for more flexibility. */

interval(+A, ?Res) is nondet

True if A evalutes to Res. Atoms, numbers, and strings are not evaluated. Supported operations:

Comparison: '>', '<', '>=', '=<', '=\=', '=:='
Basic arithemtic: addition '+', subtraction '-', division '/', multiplication '*'
Square root for positive interval: 'interval(sqrt(A), Res)'
Square root for negative or mixed interval: 'interval(sqrt1(A), Res)'
Power: 'interval(A^atomic(N), Res)' or 'interval(A**atomic(N), Res)' with N being a natural number
Exponential: 'interval(exp(A)), Res)'
Absolute value: 'interval(abs(A), Res)'
Sine: 'interval(sin(A), Res)'
Unary plus: 'interval(+(A), Res)'
Unary minus: 'interval(-(A), Res)'
Max: 'interval(max(A, B), Res)'
Min: 'interval(min(A, B), Res)'
Rounding: 'interval(round(1.356...1.634, atomic(2)), Res)'

Arguments:

`A`	- is the expression to be evaluted.
`Res`	- is the result. This should always be unbound. For checking results, use 'interval(1...2 + 1, `Res`), `Res` = 2...3' instead of 'interval(1...2 + 1, 2...3)'

   32:- set_prolog_flag(float_overflow, infinity).   33:- set_prolog_flag(float_undefined, nan).   34:- set_prolog_flag(float_zero_div, infinity).   35
   36:- nb_setval(digits, 2).   37
   38:- consult(['../inst/prolog/lib/interface', 
   39            '../inst/prolog/lib/op', 
   40            '../inst/prolog/lib/eval',
   41            '../inst/prolog/lib/utility']).