How do I conditionally create a table in Sybase (TSQL)?

IF EXISTS (
    SELECT 1
    FROM sysobjects
    WHERE name = 'a_table'
    AND type = 'U'
)
DROP TABLE a_table
GO

IF NOT EXISTS (
    SELECT 1
    FROM sysobjects
    WHERE name = 'a_table'
    AND type = 'U'
)
CREATE TABLE a_table (
    col1 int not null,
    col2 int null
)
GO

IF NOT EXISTS (
    SELECT 1
    FROM sysobjects
    WHERE name = 'a_table'
    AND type = 'U'
)
EXECUTE("CREATE TABLE a_table (
    col1 int not null,
    col2 int null
)")
GO

IF(SELECT count(*) FROM sysobjects WHERE name="tableNameWithoutUserPart") > 0
    DROP TABLE tableNameWithUserPart
GO

CREATE TABLE tableNameWithUserPart ...

IF object_id('a_table') IS NULL
BEGIN
	CREATE TABLE a_table (
		col1 int not null,
		col2 int null
	)
END