export(
       "Formula",
       "as.Formula",
       "is.Formula",
       "has.intercept"
       )

## methods for class "Formula"
S3method("formula", "Formula")
S3method("terms", "Formula")
S3method("model.frame", "Formula")
S3method("model.matrix", "Formula")
S3method("update", "Formula")
S3method("length", "Formula")

## methods to as.Formula()
S3method("as.Formula", "default")
S3method("as.Formula", "formula")

## methods to as.Formula()
S3method("has.intercept", "formula")
S3method("has.intercept", "Formula")
