g =
<=0 <=-1 <=-1
<=4 <=0 < inf
<=4 < inf <=0;

b=
<=0 <=0 <=-2
<=2 <=0 < inf
<=3 < inf <=0;

f = down(g)-(down(b)-down((g-b)&down(b)));
p = predt(g,b);

// Good:
g;
// Bad:
b;
// Formula:
f;
// predt:
p;
// OK?
f == p;

g =
<=0     <=-4    <=-9    <=-36
<=4     <=0     <=-5    <=-32
<=9     <=5     <=0     <=-27
<=36    <=32    <=27    <=0;

b =
<=0     <=-4    <=-9    <-36
<=4     <=0     <=-5    <-32
<=14    <=10    <=0     <=-27
<=41    <=37    <=32    <=0;

f = down(g)-(down(b)-down((g-b)&down(b)));
p = predt(g,b);

// Didier's good:
g;
// Didier's bad:
b;
// Formula:
f;
// predt:
p;
// OK?
f == p;

quit;