[Groff] eqn troubles

[Miklos Somogyi]

I worked with eqn quite a lot in troff days of past-not-so-perfect. It  
was rather easy to use.
Now I try my luck with groff's eqn and can't get anything going.
A simple groff program like this:

.EQ
x = y + z
.EN
.ex

indicates a syntax error. No matter what is between .EQ and .EN, it is  
syntax error.

If I .so e.tmac (where definitions of .EQ and EN are?), it does not  
matter.

If I use eqn alone or via `groff -set -I ...', the result is the same.

The $...$ inline thing is not working either.

Certainly I missed something fundamental, but I can't figure it out  
what.

Please help,

Miklos

PS: I run version 1.19.2