Following is a demo of the task1.pl program.
?- talktome.
Right now...
the large yellow block is on the table
the large red block is on the table
the large blue block is on the table
the large green block is on the table
the small yellow block is on the table
the small red block is on the table
the small blue block is on the table
the small green block is on the table
Waiting for next inputs...
|: eat the yellow block
Error, can't understand the input.
Waiting for next inputs...
|: stack the small red block on the large blue block
Right now...
the large yellow block is on the table
the large red block is on the table
the large blue block is on the table
the large green block is on the table
the small yellow block is on the table
the small red block is on the large blue block
the small blue block is on the table
the small green block is on the table
Waiting for next inputs...
|: pickup the large blue block
Error, failed to resolve reference.
Waiting for next inputs...
|: exit
false.