diff --git a/References/Goodson_2012.pdf b/References/Goodson_2012.pdf
new file mode 100644
index 0000000..7940225
Binary files /dev/null and b/References/Goodson_2012.pdf differ
diff --git a/References/Goodson_2019.pdf b/References/Goodson_2019.pdf
new file mode 100644
index 0000000..effd17b
Binary files /dev/null and b/References/Goodson_2019.pdf differ
diff --git a/References/Surjan_2000.pdf b/References/Surjan_2000.pdf
new file mode 100644
index 0000000..49d5693
Binary files /dev/null and b/References/Surjan_2000.pdf differ