Cannot build symbc

[karlskrol]

Hi, I success in running example in jpf-core but when I build symbc by
typing:
/jpf-symbc$ bin/ant test
it returns:
ERROR: no ant.jar found in known tools dirs (check your
site.properties)

In the file site.properties, I wrote:
# JPF site configuration
jpf-core=~/Jpathfiner/jpf-core

# numeric extension
jpf-numeric = ~/Jpathfiner/jpf/jpf-numeric

# annotation-based program properties extension
jpf-aprop = ~/Jpathfiner/jpf/jpf-aprop

extensions=${jpf-core},${jpf-aprop}

jpf-symbc = ~/Jpathfiner/jpf-symbc
extensions+=,${jpf-symbc}

Could you give me some help!