#6 compiling request flex 2.5 33, installed is 2.6.1

[Carlo Vinante]

Hello everybody

we are going to installa Phoebe on two PCs. one with Debian 9 64bit and another with Ubuntu
Started on compiling the Phoebe libs (executing ./configure) at the end of the process it claims about flex; it needs flex 2.5.33 but in the system the 2.6.1 is already installed.

How can we fix this problem ?
Many thanks
Regards

Carlo

attached a txt file with the output generated by ./configure during the compiling process