sol --variation freecell Backtrace: In /usr/share/sol-games/freecell.scm: 581: 0* (define kill-thread-mutex (make-mutex)) 581: 1* (make-mutex) /usr/share/sol-games/freecell.scm:581:27: In expression (make-mutex): /usr/share/sol-games/freecell.scm:581:27: Unbound variable: make-mutex