Bugfix monotonicity pt

[jeremyirilli]

pt is always increasing, so no need to find the maximum.

pt(seq(-3, 3, 0.3), 2)
 [1] 0.04773298 0.05707937 0.06922510 0.08527493 0.10683317 0.13619656
 [7] 0.17650168 0.23155251 0.30471663 0.39624283 0.50000000 0.60375717
[13] 0.69528337 0.76844749 0.82349832 0.86380344 0.89316683 0.91472507
[19] 0.93077490 0.94292063 0.95226702

Before

?- interval(pt(-0.5, 5...6), Res).
Res = 0.3191494358204645...0.31744.  %wrong

?- interval(pt(-0.5...0.2, 2...5, true), Res).
Res = 0.5...0.6808505641795355.

After

?- interval(pt(-0.5, 5...6), Res).
Res = 0.31744...0.3191494358204645.

interval(pt(-0.5...0.2, 2...5, true), Res).
Res = 0.3191494358204645...0.5753197430020855.

 pt(-0.5, 5)
[1] 0.3191494
pt(-0.5, 6)
[1] 0.31744


pt(-0.5, 2)
[1] 0.3333333
pt(-0.5, 5)
[1] 0.3191494
pt(0.2, 2)
[1] 0.570014
pt(0.2, 5)
[1] 0.5753197