[see also: customary, familiar, usual
The functions fi (i=1,…,n) have no common zero in Ω.
Then F and G have a factor in common.
It has some basic properties in common with another most important class of functions, namely, the continuous ones.
Take g1,…,gn without common zero.
Denote by θ the angle at x which is common to these triangles.
The endpoint common to A and B will be called the free endpoint of N.