http://catalogo.fi.uba.ar/cgi-bin/koha/opac-search.pl?q=ccl=au%3AWillerding%2C%20Margaret%20F.%20and%20su-to%3APROBLEMAS%20and%20su-to%3ASISTEMAS%20DE%20NUMERACION&format=rss2 2 0 50 ISBN http://catalogo.fi.uba.ar/cgi-bin/koha/opac-detail.pl?biblionumber=2623 México : Trillas, 1964 . 45 p. : , Tít. orig.: Topics in mathematics for elementary school teachers. Booklet number 4 : algorithms for operations with whole numbers 23 cm.

]]> http://catalogo.fi.uba.ar/cgi-bin/koha/opac-detail.pl?biblionumber=2623 ISBN http://catalogo.fi.uba.ar/cgi-bin/koha/opac-detail.pl?biblionumber=2626 México : Trillas, 1968 . 59 p. : , Tít. orig.: Topics in mathematics for elementary school teachers 23 cm.

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