@conference {cVallverdu02,
	title = {Graphical study of signals and systems},
	booktitle = {14th annual World Conference on Educational Multimedia, Hypermedia \& Telecommunications},
	year = {2002},
	isbn = {0-8186-7919-0},
	author = {Vallverdu, F. and Elisa Sayrol and Gasull, A. and Salavedra, J. and Moreno, A.}
}
@conference {cSayrol01a,
	title = {Graphical Study of Signals and Systems},
	booktitle = {International Conference on Acoustics, Speech and Signal Processing ICASSP{\textquoteright}01},
	year = {2001},
	isbn = {0-7803-1775-0},
	author = {Elisa Sayrol and Gasull, A. and Moreno, A. and Salavedra, J. and Vallverdu, F.}
}
