[erlang-questions] Concurrent Programing in Erlang

[kg9020@REDACTED]

The example given Program 9.2 and Program 9.3
when run gives a 1> demo_server:start().
sh: line 1: exec: demo_server: not found

The programs are both in the same directory and other tutorial programs run
... am  I missing something

the coding follows the examples put forth in the pdf

thanks
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