Michael Baldamus Joachim Parrow Björn Victor Spi Calculus Translated to ?--Calculus Preserving May-Tests. 22-31 2004 conf/lics/2004 LICS http://csdl.computer.org/comp/proceedings/lics/2004/2192/00/21920022abs.htm db/conf/lics/lics2004.html#BaldamusPV04