diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
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--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -270,8 +270,6 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 
 ### APL
 
-* [A Practical Introduction to APL1 & APL2](http://robertson.uk.net/Files/APL1&2.pdf) - Graeme Donald Robertson (PDF)
-* [A Practical Introduction to APL3 & APL4](http://robertson.uk.net/Files/APL3&4.pdf) - Graeme Donald Robertson (PDF)
 * [APL2 at a glance](https://ia801009.us.archive.org/28/items/apl-2-at-a-glance-brown-pakin-polivka/APL2_at_a_Glance_-_Brown_Pakin_Polivka.pdf) - James A. Brown, Sandra Pakin, Raymond P. Polivka - 1988 (PDF) *(:card_file_box: archived)*
 * [Introduction to College Mathematics with A Programming Language (1978)](http://www.softwarepreservation.org/projects/apl/Books/CollegeMathematicswithAPL) - E. J. LeCuyer (PDF)
 * [Learning APL](https://xpqz.github.io/learnapl) - Stefan Kruger (HTML,PDF,IPYNB)