SQL Alias error?

I keep getting this error: Whenever a table alias is defined, kindly use table alias name before the respective columns used in SELECT query

I don't know where I've went wrong.

SELECT Distinct "Book Title",

t1."Author" as 'Authors1',

t2."Author" as 'Authors2',

FROM "SET1" t1

LEFT JOIN "SET2" t2

ON t1."Book Title" = t2."Book Title"

WHERE Authors1 LIKE '%John%'

OR Authors2 LIKE '%John%'