Third line of program, set ia.airplanes does not end with a semicolon as it should. The SET statement of SAS is used to read data from dataset(s). When SAS compiles this statement, all tokens after SET will be assumed as SAS datasets; thus, SAS looks for datasets named IF, MPG, GT, THEN, and OUTPUT (at which point it sees the end of the SET statement with a semicolon). Since these are not available datasets, SAS reports an error and stops execution.
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