Example found in the 2007.03 Liberty Reference Manual that was also found
in the wild:

    input_voltage(CMOS) {
        vil : 0.3 * VDD ;
        vih : 0.7 * VDD ;
        vimin : -0.5 ;
        vimax : VDD + 0.5 ;
    }

Current implementation just parses the expression but no interpretation is done.

Usage:

Starting from an empty directory:

(1) set AS to point to the location of ABC

(2) reconstruct the directory structure of ABC in the new directory:

    mkdir -p `cd $AS && find src -type d`

(3) Build ABC:

    make -f $AS/Makefile VPATH=$AS ABCSRC=$AS